Regular ingestion of tea does not inhibit in vivo lipid peroxidation in humans

Green tea extract-biomembrane interaction study: The role of its two major components, (-)-epigallocatechin gallate and (-)-epigallocatechin

The interaction of antioxidants with biological membranes is closely related with their efficacy to inhibit the lipid peroxidation, the cause of several pathologies including cancer, neurodegenerative and cardiovascular disorders. Despite being pointed as a promising antioxidant agent by some authors, the anti-lipid peroxidation of green tea extract (GTE) has not aroused consensus among the scientific community. Since the interaction of drugs with biological membranes plays a key role on their therapeutic activity, this study aims to evaluate the interaction of GTE with liposomes as in vitro biomembrane models composed of 1,2-dimyristoyl-sn-glycero-3-phosphocholine phospholipids in the absence and presence of cholesterol (CHOL) (15 mol%). The affinity of GTE and its main components (-)-epigallocatechin gallate (EGCG) and (-)-epigallocatechin (EGC) to the lipid bilayer, their membrane location as well as their effect on the membrane fluidity was investigated by diverse biophysical techniques. Derivative spectrophotometry results proved that GTE has high affinity to the membrane by establishing hydrophobic interactions with the non-polar region of phospholipids and electrostatic interactions with the polar phospholipid heads. Fluorescence and dynamic light scattering data confirm that GTE is located in both hydrophobic and hydrophilic regions of the lipid membrane, therefore affecting the structure of the biomembrane by increasing its fluidity. However, the increased stiffness and organization of the lipid bilayer caused by CHOL significantly affected the interaction of GTE with the membrane. Moreover, the obtained findings suggest a direct contribution of EGCG and EGC on the GTE-membrane interaction.

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.

Suppression of DNA/RNA and protein oxidation by dietary supplement which contains plant extracts and vitamins: a randomized, double-blind, placebo-controlled trial

Background

Excessive oxidative stress may impair bio-molecules and cellular function. Multi antioxidant supplementation is thought to be more effective than a single antioxidant probably through the synergistic or complementary action of natural substances that could enhance the prospective effect.

Methods

In order to estimate the effect of a plant extract based supplement in apparently healthy volunteers’ oxidative stress markers, a double-blind and placebo controlled intervention was performed. 62 apparently healthy volunteers, overweight with medium adherence to the Mediterranean diet, were recruited and randomly allocated into two intervention groups (supplement or placebo) for 8 weeks. Basic biochemical markers, oxidized LDL (oxLDL), resistance of serum in oxidation, protein carbonyls in serum and 8-isoprostane and DNA/RNA damage in urine were measured.

Results

No differentiation was observed in basic biochemical markers, in oxLDL levels as well as in serum resistance against oxidation, during intervention in the examined groups. A significant resistance regarding urine isoprostanes levels in the supplement group compared to the placebo one, was observed. Reduction on DNA/RNA damage and on protein carbonyls levels (almost 30% and 20% respectively, at 8 weeks) was detected in volunteers who consumed the supplement compared to the control group.

Conclusion

Consumption of plant extract based supplement seems to reduce DNA/RNA and protein oxidation and in less extent lipids peroxidation.

Trial registration

ClinicalTrials.gov Identifier for this study is: NCT02837107.

Strategies to decrease oxidative stress biomarker levels in human medical conditions: A meta-analysis on 8-iso-prostaglandin F2α

The widespread detection of elevated oxidative stress levels in many medical conditions has led to numerous efforts to design interventions to reduce its effects. Efforts have been wide-ranging, from dietary changes to administration of antioxidants, supplements, e.g., omega-3-fatty acids, and many medications. However, there is still no systemic assessment of the efficacy of treatments for oxidative stress reduction across a variety of medical conditions. The goal of this meta-analysis is, by combining multiple studies, to quantitate the change in the levels of the popular oxidative stress biomarker 8-iso-prostaglandin F2α (8-iso-PGF2α) after a variety of treatment strategies in human populations. Nearly 350 unique publications with 180 distinct strategies were included in the analysis. For each strategy, the difference between pre- or placebo and post-treatment levels calculated using Hedges' g value of effect. In general, administration of antibiotics, antihyperlipidemic agents, or changes in lifestyle (g = - 0.63, - 0.54, and 0.56) had the largest effect. Administration of supplements, antioxidants, or changes in diet (g = - 0.09, - 0.28, - 0.12) had small quantitative effects. To fully interpret the effectiveness of these treatments, comparisons to the increase in g value for each medical condition is required. For example, antioxidants in populations with coronary artery disease (CAD) reduce the 8-iso-PGF2α levels by g = - 0.34 ± 0.1, which is quantitatively considered a small effect. However, CAD populations, in comparison to healthy populations, have an increase in 8-iso-PGF2α levels by g = 0.38 ± 0.04; therefore, the overall reduction of 8-iso-PGF2α levels is ≈ 90% by this treatment in this specific medical condition. In conclusion, 8-iso-PGF2α levels can be reduced not only by antioxidants but by many other strategies. Not all strategies are equally effective at reducing 8-iso-PGF2α levels. In addition, the effectiveness of any strategy can be assessed only in relation to the medical condition investigated.

Nutritional Supplements for the Treatment of Hypertension: A Practical Guide for Clinicians

Nutraceuticals are dietary components with pharmacologic properties that can be used to treat various disease states. There is growing interest among patients in the use of nutraceuticals for the management of hypertension; as such, it is important that clinicians are prepared to engage in meaningful discussions with their patients about these substances. Flavonoids, beetroot, garlic, and unsaturated fats have garnered significant attention for their blood pressure lowering properties. We review the clinical evidence and reported mechanisms of action for these substances in an attempt to offer a practical guide for clinicians to engage with patients who are highly motivated to seek out nutraceutical therapies to manage their hypertension.

Antioxidants from black and green tea: from dietary modulation of oxidative stress to pharmacological mechanisms

The consumption of tea (Camellia sinensis) has been correlated with a low incidence of chronic pathologies, such as cardiovascular disease and cancer, in which oxidative stress plays a critical role. Tea catechins and theaflavins are, respectively, the bioactive phytochemicals responsible for the antioxidant activity of green tea (GT) and black tea (BT). In addition to their redox properties, tea catechins and theaflavins could have also pharmacological activities, such as the ability to lower glucose, lipid and uric acid (UA) levels. These activities are mediated by pharmacological mechanisms such as enzymatic inhibition and interaction with transporters. Epigallocatechin gallate is the most active compound at inhibiting the enzymes involved in cholesterol and UA metabolism (hydroxy-3-methyl-glutaryl-CoA reductase and xanthine oxidase respectively) and affecting glucose transporters. The structural features of catechins that significantly contribute to their pharmacological effect are the presence/absence of the galloyl moiety and the number and positions of the hydroxyl groups on the rings. Although the inhibitory effects on α-glucosidase, maltase, amylase and lipase, multidrug resistance 1, organic anion transporters and proton-coupled folate transport occur at higher concentrations than those apparent in the circulation, these effects could be relevant in the gut. In conclusion, despite the urgent need for further research in humans, the regular consumption of moderate quantities of GT and BT can effectively modulate their antioxidant capacity, mainly in people subjected to oxidative stress, and could improve the metabolism of glucose, lipid and UA.

LINKED ARTICLES

This article is part of a themed section on Principles of Pharmacological Research of Nutraceuticals. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.11/issuetoc.

Green Tea and Bone Marrow Transplantation: From Antioxidant Activity to Enzymatic and Multidrug-resistance Modulation

Epigallocatechin-3-gallate (EGCG), the main flavonoid of green tea (GT), could play an active role in the prevention of oxidative-stress-related diseases, such as hematologic malignancies. Some effects of EGCG are not imputable to antioxidant activity, but involve modulation of antioxidant enzymes and uric acid (UA) levels. The latter is the major factor responsible of the plasma non-enzymatic antioxidant capacity (NEAC). However, hyperuricemia is a frequent clinical feature caused by tumor lysis syndrome or cyclosporine side effects, both before and after bone marrow transplantation (BMT). Besides this, food-drug interactions could be associated with GT consumption and could have clinical implications. The molecular mechanisms involved in the redox and drug metabolizing/transporting pathways were discussed, with particular reference to the potential role of GT and EGCG in BMT. Moreover, on reviewing data on NEAC, isoprostanes, uric acid, and various enzymes from human studies on GT, its extract, or EGCG, an increase in NEAC, without effect on isoprostanes, and contrasting results on UA and enzymes were observed. Currently, few and contrasting available evidences suggest caution for GT consumption in BMT patients and more studies are needed to better understand the potential impact of EGCG on oxidative stress and metabolizing/transporting systems.

Effects of tea intake on blood pressure: a meta-analysis of randomised controlled trials

The effect of tea intake on blood pressure (BP) is controversial. We performed a meta-analysis of randomised controlled trials to determine the changes in systolic and diastolic BP due to the intake of black and green tea. A systematic search was conducted in MEDLINE, EMBASE and the Cochrane Controlled Trials Register up to May 2014. The weighted mean difference was calculated for net changes in systolic and diastolic BP using fixed-effects or random-effects models. Previously defined subgroup analyses were performed to explore the influence of study characteristics. A total of twenty-five eligible studies with 1476 subjects were selected. The acute intake of tea had no effects on systolic and diastolic BP. However, after long-term tea intake, the pooled mean systolic and diastolic BP were lower by - 1·8 (95 % CI - 2·4, - 1·1) and - 1·4 (95 % CI - 2·2, - 0·6) mmHg, respectively. When stratified by type of tea, green tea significantly reduced systolic BP by 2·1 (95 % CI - 2·9, - 1·2) mmHg and decreased diastolic BP by 1·7 (95 % CI - 2·9, - 0·5) mmHg, and black tea showed a reduction in systolic BP of 1·4 (95 % CI - 2·4, - 0·4) mmHg and a decrease in diastolic BP of 1·1 (95 % CI - 1·9, - 0·2) mmHg. The subgroup analyses showed that the BP-lowering effect was apparent in subjects who consumed tea more than 12 weeks (systolic BP - 2·6 (95 % CI - 3·5, - 1·7) mmHg and diastolic BP - 2·2 (95 % CI - 3·0, - 1·3) mmHg, both P< 0·001). The present findings suggest that long-term ( ≥ 12 weeks) ingestion of tea could result in a significant reduction in systolic and diastolic BP.

Effects of consumption of rooibos (Aspalathus linearis) and a rooibos-derived commercial supplement on hepatic tissue injury by tert-butyl hydroperoxide in Wistar rats

This study investigated the antioxidative effect of rooibos herbal tea and a rooibos-derived commercial supplement on tert-butyl hydroperoxide- (t-BHP-) induced oxidative stress in the liver. Forty male Wistar rats consumed fermented rooibos, unfermented rooibos, a rooibos-derived commercial supplement, or water for 10 weeks, while oxidative stress was induced during the last 2 weeks via intraperitoneal injection of 30 µmole of t-BHP per 100 g body weight. None of the beverages impaired the body weight gain of the respective animals. Rats consuming the rooibos-derived commercial supplement had the highest (P < 0.05) daily total polyphenol intake (169 mg/day) followed by rats consuming the unfermented rooibos (93.4 mg/day) and fermented rooibos (73.1 mg/day). Intake of both the derived supplement and unfermented rooibos restored the t-BHP-induced reduction and increased (P < 0.05) the antioxidant capacity status of the liver, while not impacting on lipid peroxidation. The rooibos herbal tea did not affect the hepatic antioxidant enzymes, except fermented rooibos that caused a decrease (P < 0.05) in superoxide dismutase activity. This study confirms rooibos herbal tea as good dietary antioxidant sources and, in conjunction with its many other components, offers a significantly enhanced antioxidant status of the liver in an induced oxidative stress situation.

Green and black tea for the primary prevention of cardiovascular disease

BACKGROUND

There is increasing evidence that both green and black tea are beneficial for cardiovascular disease (CVD) prevention.

OBJECTIVES

To determine the effects of green and black tea on the primary prevention of CVD.

SEARCH METHODS

We searched the following databases on 12 October 2012 without language restrictions: CENTRAL in The Cochrane Library, MEDLINE (OVID), EMBASE (OVID) and Web of Science (Thomson Reuters). We also searched trial registers, screened reference lists and contacted authors for additional information where necessary.

SELECTION CRITERIA

Randomised controlled trials (RCTs) lasting at least three months involving healthy adults or those at high risk of CVD. Trials investigated the intake of green tea, black tea or tea extracts. The comparison group was no intervention, placebo or minimal intervention. The outcomes of interest were CVD clinical events and major CVD risk factors. Any trials involving multifactorial lifestyle interventions or focusing on weight loss were excluded to avoid confounding.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected trials for inclusion, abstracted data and assessed the risk of bias. Trials of green tea were analysed separately from trials of black tea.

MAIN RESULTS

We identified 11 RCTs with a total of 821 participants, two trials awaiting classification and one ongoing trial. Seven trials examined a green tea intervention and four examined a black tea intervention. Dosage and form of both green and black tea differed between trials. The ongoing trial is examining the effects of green tea powder capsules.No studies reported cardiovascular events.Black tea was found to produce statistically significant reductions in low-density lipoprotein (LDL) cholesterol (mean difference (MD) -0.43 mmol/L, 95% confidence interval (CI) -0.56 to -0.31) and blood pressure (systolic blood pressure (SBP): MD -1.85 mmHg, 95% CI -3.21 to -0.48. Diastolic blood pressure (DBP): MD -1.27 mmHg, 95% CI -3.06 to 0.53) over six months, stable to sensitivity analysis, but only a small number of trials contributed to each analysis and studies were at risk of bias.Green tea was also found to produce statistically significant reductions in total cholesterol (MD -0.62 mmol/L, 95% CI -0.77 to -0.46), LDL cholesterol (MD -0.64 mmol/L, 95% CI -0.77 to -0.52) and blood pressure (SBP: MD -3.18 mmHg, 95% CI -5.25 to -1.11; DBP: MD -3.42, 95% CI -4.54 to -2.30), but only a small number of studies contributed to each analysis, and results were not stable to sensitivity analysis. When both tea types were analysed together they showed favourable effects on LDL cholesterol (MD -0.48 mmol/L, 95% CI -0.61 to -0.35) and blood pressure (SBP: MD -2.25 mmHg, 95% CI -3.39 to -1.11; DBP: MD -2.81 mmHg, 95% CI -3.77 to -1.86). Adverse events were measured in five trials and included a diagnosis of prostate cancer, hospitalisation for influenza, appendicitis and retinal detachment but these are unlikely to be directly attributable to the intervention.

AUTHORS' CONCLUSIONS

There are very few long-term studies to date examining green or black tea for the primary prevention of CVD. The limited evidence suggests that tea has favourable effects on CVD risk factors, but due to the small number of trials contributing to each analysis the results should be treated with some caution and further high quality trials with longer-term follow-up are needed to confirm this.

Nutrition and oxidative stress: a systematic review of human studies

Oxidative stress (OS) - defined as the imbalance between free radical production and antioxidant defences - is a condition associated with chronic-degenerative disease, such as cancer, metabolic and disease cardiovascular diseases (CVDs). Several studies have shown that diet and some of its components could influence the intensity of OS damage. The aim of this review was to critically examine some pieces of evidence from observational and intervention study in human beings to assess whether diet and its components can really modify OS in vivo. Furthermore, we tried to find out the possible mechanism behind this association. We considered all studies in MEDLINE which fitted with the following criteria: (1) adult subjects who were healthy or affected by metabolic disease and CVDs; (2) no food supplements, pillows, powder but only common foods and beverages and (3) OS assessment with well-known and validated in vivo biomarkers.

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.

Major metabolite of F2-isoprostane in urine may be a more sensitive biomarker of oxidative stress than isoprostane itself

BACKGROUND

There is limited literature on the contributors to isoprostane metabolite 2,3-dinor-5,6-dihydro-15-F(2t)-isoprostane (15-F(2t)-IsoP-M) compared with F(2)-isoprostanes (F(2)-IsoPs) as an oxidative stress biomarker.

OBJECTIVE

The objective of this study was to investigate whether plasma concentrations of antioxidants, urinary excretion rates of polyphenols, and antioxidants in food and dietary supplements are attributable to both urinary F(2)-IsoP and 15-F(2t)-IsoP-M concentrations.

DESIGN

Dietary intake information and blood and urine samples were obtained from 845 healthy middle-aged and elderly female participants of the Shanghai Women's Health Study. Urinary isoprostanes (F(2)-IsoPs and 15-F(2t)-IsoP-M) were measured and adjusted for creatinine concentrations.

RESULTS

Urinary 15-F(2t)-IsoP-M and F(2)-IsoP concentrations were lower in subjects who used a multivitamin. Lower F(2)-IsoP concentrations were observed in ginseng users, whereas lower concentrations of 15-F(2t)-IsoP-M were shown in subjects who used a vitamin E supplement. Plasma concentrations of several antioxidants (ie, β-carotenes, both trans and cis β-carotenes, lycopene other than trans, 5-cis and 7-cis isomers, cis anhydrolutein, and cis β-cryptoxanthin) were inversely associated with 15-F(2t)-IsoP-M but not with F(2)-IsoPs, whereas β-, γ-, and δ-tocopherols were positively associated with 15-F(2t)-IsoP-M but not with F(2)-IsoPs. Urinary polyphenol quercetin was positively associated with both F(2)-IsoPs and 15-F(2t)-IsoP-M.

CONCLUSION

The results suggest that the F(2)-IsoP major metabolite 15-F(2t)-IsoP-M may be a more sensitive marker of endogenous oxidative stress status than are F(2)-IsoPs in the assessment of effects of antioxidants on age-related diseases.

Consumption of green tea or green tea products: is there an evidence for antioxidant effects from controlled interventional studies?

PURPOSE

Epidemiological data suggest that green tea (GT) consumption may protect against cardiovascular diseases (CVDs) and different types of cancer. This effect is attributed primarily to the antioxidant properties of flavanols from GT. This review provides an overview of controlled intervention studies investigating the effect of GT consumption on antioxidant effects ex vivo and in vivo.

METHODS

The Medline and Cochrane databases were searched independently by two investigators for controlled intervention studies (English) on GT consumption and antioxidant effects published up to June 2010. Thirty-one studies investigating antioxidant effects ex vivo [plasma antioxidant capacity (AC), DNA's resistance against oxidative induced damage) or in vivo (lipid and protein oxidation, DNA damage] met the criteria. Results were compared by considering the participants, the dose of GT, the amount of ingested flavanols, the duration of supplementation and the investigated biomarkers.

RESULTS

The comparison between the studies was difficult as relevant data, e.g., on flavanol concentration in plasma (10 of 31 studies) or on major antioxidants contributing to AC, were often missing. Lipid peroxidation and DNA damage were commonly investigated. Data on protein oxidation are scarce. An antioxidant effect of at least one parameter (increase in AC or reduction of oxidative stress marker) was observed in 15 out of 22 studies by daily consumption of GT, primarily in participants exposed to oxidative stress (smokers or mixed collectives of smokers and non-smokers and physical activity) and in 6 out of 9 studies investigating the bolus consumption of GT.

CONCLUSION

There is limited evidence that regular consumption of GT in amounts of at least 0.6-1.5 l/day may increase AC and reduce lipid peroxidation (especially oxidation of LDL). This may contribute to the protection against CVDs and different types of cancer. Beneficial effects seem to be more likely in participants exposed to oxidative challenge.

Green tea intake lowers fasting serum total and LDL cholesterol in adults: a meta-analysis of 14 randomized controlled trials

BACKGROUND

The effect of green tea beverage and green tea extract on lipid changes is controversial.

OBJECTIVE

We aimed to identify and quantify the effect of green tea and its extract on total cholesterol (TC), LDL cholesterol, and HDL cholesterol.

DESIGN

We performed a comprehensive literature search to identify relevant trials of green tea beverages and extracts on lipid profiles in adults. Weighted mean differences were calculated for net changes in lipid concentrations by using fixed-effects or random-effects models. Study quality was assessed by using the Jadad score, and a meta-analysis was conducted.

RESULTS

Fourteen eligible randomized controlled trials with 1136 subjects were enrolled in our current meta-analysis. Green tea consumption significantly lowered the TC concentration by 7.20 mg/dL (95% CI: -8.19, -6.21 mg/dL; P < 0.001) and significantly lowered the LDL-cholesterol concentration by 2.19 mg/dL (95% CI: -3.16, -1.21 mg/dL; P < 0.001). The mean change in blood HDL-cholesterol concentration was not significant. Subgroup and sensitivity analyses showed that these changes were not influenced by the type of intervention, treatment dose of green tea catechins, study duration, individual health status, or quality of the study. Overall, no significant heterogeneity was detected for TC, LDL cholesterol, and HDL cholesterol; and results were reported on the basis of fixed-effects models.

CONCLUSION

The analysis of eligible studies showed that the administration of green tea beverages or extracts resulted in significant reductions in serum TC and LDL-cholesterol concentrations, but no effect on HDL cholesterol was observed.

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).

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.

Effects of Yerba Mate (Ilex paraguariensis) supplementation on the performance of dairy calves

Yerba Mate (Ilex paraguariensis), a tea known for its high antioxidant content, was supplemented to 24 of 48 Holstein calves to assess its effect on the calves’ performance. Calves were weighed and blood samples were taken each week. Serum was assayed for metabolic parameters (total protein, albumin, urea, non-esterified fatty acids, triglycerides and β-hydroxybutyric acid) and markers of oxidative status [advanced oxidation protein products, 8-isoprostane and total antioxidant capacity (TAC) concentration]. Supplemented calves had higher triglyceride levels (P < 0.05) suggesting that Yerba Mate induced fat mobilisation and usage. A significant effect of the interaction time of sampling × diet (P < 0.05) was noted for plasma TAC concentration with the Yerba mate calves presenting significantly lower levels of TAC on the last week of the trial. Yerba Mate supplemented calves had significantly lower levels of total protein (P < 0.05) and albumin (P < 0.05) compared with the non-supplemented calves. The net result was reduced liveweight in Yerba Mate supplemented calves (P < 0.001) and thus the hypothesis that Yerba Mate supplementation would increase dairy calves’ growth rates was rejected. This study demonstrated that supplementation of Yerba Mate to dairy calves had significant effects on their metabolic and oxidative status, which resulted in lower liveweight at the end of the trial.

Effect of daily fruit ingestion on angiotensin converting enzyme activity, blood pressure, and oxidative stress in chronic smokers

OBJECTIVE

This study examined whether, daily fruit (blueberries) consumption (250 g) for three weeks or acute fruit ingestion (250 g) would attenuate angiotensin converting enzyme (ACE) activity and reduce oxidative stress in chronic cigarette smokers.

METHODS

Twenty subjects were recruited and randomized into fruit or control groups. Blood samples and blood pressure were obtained at baseline and then pre and one hour post when subjects returned to the lab three weeks later. To examine acute effects, the fruit group immediately ingested 250 g of blueberries after returning and at least one hour prior to the post blood draw. Plasma samples were analyzed for ACE activity, F(2)- isoprostanes and lipid hydroperoxides (LH) as measures of oxidative stress, and ferric reducing ability of plasma (FRAP) as a measure of antioxidant potential. A 2 (treatment) x 3 (time) repeated measures ANOVA was used for statistical analysis. If interaction was significant, then Student's t-tests were used to further examine this relationship. For these comparisons, a Bonferroni adjustment was made with statistical significance set at P < 0.025.

RESULTS

The pattern of change between treatments was not significant for any variable except LH (P < 0.001).

CONCLUSION

This study indicates that LH are significantly reduced by daily fruit consumption, but not affected by acute ingestion. This finding could be one way in which fruit consumption contributes to prevention of cardiovascular disease.

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

BACKGROUND

Dietary flavonoids may improve endothelial function and ultimately lead to beneficial cardiovascular effects.

OBJECTIVE

The objective was to assess whether pure dietary flavonoids can modulate nitric oxide and endothelin-1 production and thereby improve endothelial function.

DESIGN

A randomized, placebo-controlled, crossover trial in 12 healthy men was conducted to compare the acute effects of the oral administration of 200 mg quercetin, (-)-epicatechin, or epigallocatechin gallate on nitric oxide, endothelin-1, and oxidative stress after nitric oxide production was assessed via the measurement of plasma S-nitrosothiols and plasma and urinary nitrite and nitrate concentrations. The effects on oxidative stress were assessed by measuring plasma and urinary F(2)-isoprostanes. Plasma and urinary concentrations of quercetin, (-)-epicatechin, and epigallocatechin gallate were measured to establish the absorption of these flavonoids.

RESULTS

Relative to water (control), quercetin and (-)-epicatechin resulted in a significant increase in plasma S-nitrosothiols, plasma nitrite, and urinary nitrate concentrations (P < 0.05), but not in plasma nitrate or urinary nitrite. Epigallocatechin gallate did not alter any of the measures of nitric oxide production. Quercetin and (-)-epicatechin resulted in a significant reduction in plasma endothelin-1 concentration (P < 0.05), but only quercetin significantly decreased the urinary endothelin-1 concentration. None of the 3 treatments significantly changed plasma or urinary F(2)-isoprostane concentrations. Significant increases in the circulating concentrations of the 3 flavonoids were observed (P < 0.05) after the corresponding treatment.

CONCLUSIONS

Dietary flavonoids, such as quercetin and (-)-epicatechin, can augment nitric oxide status and reduce endothelin-1 concentrations and may thereby improve endothelial function.

The relation between green tea consumption and cardiovascular disease as evidenced by epidemiological studies

Although substantial evidence from in vitro and animal studies indicates that green tea preparations inhibit cardiovascular disease processes, the possible protective role of green tea consumption against this disease in humans remains unclear. We conducted a population-based prospective cohort study (the Ohsaki Study) to examine the association between green tea consumption and mortality from cardiovascular disease (CVD), cancer, and all causes with 40,530 persons in Miyagi prefecture, in northern Japan. Previously published work has shown that green tea consumption was inversely associated with mortality from CVD and all causes. The inverse association of mortality from CVD was more pronounced in women (P = 0.08 for interaction with sex). In women, the multivariate hazard ratios (95% confidence intervals) of CVD mortality across increasing green tea consumption categories were 1.00, 0.84 (0.63-1.12), 0.69 (0.52-0.93), 0.69 (0.53-0.90) (P for trend = 0.004). Within CVD mortality, the stronger inverse association was observed for stroke mortality. Because our observational study has found the inverse association, I report here the results of a review of epidemiological evidence from randomized controlled trials (RCT) of the association between green tea or green tea extracts and CVD risk profiles. More than half of the RCT have demonstrated the beneficial effects of green tea on CVD risk profiles. These results from RCT suggest a plausible mechanism for the beneficial effects of green tea and provide substantial support for our observations.

How to understand the dichotomy of antioxidants

One of the most bewildering aspects of antioxidants is that their excellent in vitro activity cannot necessarily be translated into in vivo effect. Through summarizing the recent progresses made in free radical chemistry and biology, this dichotomy is tentatively explained in terms of the heterogeneity of biological systems and the interactions between antioxidants and surrounding molecules in vivo, which also has important implications for updating the current strategies for screening and designing antioxidant drugs.

A 6-month randomized pilot study of black tea and cardiovascular risk factors

BACKGROUND

The effects of black tea consumption on cardiovascular risk factors have been inconsistent in previous randomized trials, all of which have been limited to a few weeks duration.

METHODS

We conducted a pilot parallel-design randomized controlled trial among 31 adults aged 55 years and older with either diabetes or 2 other cardiovascular risk factors but no established clinical cardiovascular disease. Participants were randomized to drink 3 glasses daily of either a standardized black tea preparation or water for 6 months. Cardiovascular risk factors were measured at the beginning and conclusion of the study.

RESULTS

Three participants dropped out of the study, leaving 14 participants assigned to tea and 14 assigned to water eligible for analyses. We found no statistically significant effects of black tea on cardiovascular biomarkers, including lipids, inflammatory markers, hemoglobin, adhesion molecules, prothrombotic and fibrinolytic parameters, and lipoprotein oxidizability. Assignment to tea did not appreciably influence blood pressure, and heart rate among participants assigned to tea was marginally higher than among control participants at 3 months (P = .07) but not 6 months.

CONCLUSIONS

In this randomized trial of black tea intake over 6 months among older adults with known cardiovascular risk factors, black tea did not appreciably influence any traditional or novel biomarkers of cardiovascular risk. Longer randomized trials are needed to verify the inverse association of tea with risk of cardiovascular disease seen in cohort studies and identify potential candidate mechanisms for such an association.

Effects of Flavonoid-Containing Beverages and EGCG on Endothelial Function

Abnormalities of the vascular endothelium contribute to all stages of atherosclerosis from lesion development to clinical cardiovascular disease events. Recognized risk factors, including diabetes mellitus, hypertension, dyslipidemia, cigarette smoking, and sedentary lifestyle are associated with endothelial dysfunction. A variety of pharmacological and behavioral interventions have been shown to reverse endothelial dysfunction in patients with cardiovascular disease. A large number of epidemiological studies suggest that dietary factors, including increased intake of flavonoid-containing foods and beverages, reduce cardiovascular risk, and recent studies have shown that such beverages have favorable effects on endothelial function. These studies have engendered interest in the development of dietary supplements or drugs that would allow for more convenient and higher dose administration of flavonoids and might prove useful for prevention or treatment of cardiovascular disease. In this paper, we will review the contribution of endothelial dysfunction to the pathogenesis and clinical expression of atherosclerosis and recent data linking flavonoid and EGCG consumption to improved endothelial function and reduced cardiovascular risk.

Green tea as inhibitor of the intestinal absorption of lipids: potential mechanism for its lipid-lowering effect

Animal and epidemiological studies suggest that green tea catechins may reduce the risk of cardiovascular diseases [e.g., coronary heart disease (CHD)]. The health benefit of green tea has been attributed to its antioxidant and anti-inflammatory properties; however, considerable evidence suggests that green tea and its catechins may reduce the risk of CHD by lowering the plasma levels of cholesterol and triglyceride. Although the mechanism underlying such effect of green tea is yet to be determined, it is evident from in vitro and in vivo studies that green tea or catechins inhibit the intestinal absorption of dietary lipids. Studies in vitro indicate that green tea catechins, particularly (-)-epigallocatechin gallate, interfere with the emulsification, digestion, and micellar solubilization of lipids, critical steps involved in the intestinal absorption of dietary fat, cholesterol, and other lipids. Based on the observations, it is likely that green tea or its catechins lower the absorption and tissue accumulation of other lipophilic organic compounds. The available information strongly suggests that green tea or its catechins may be used as safe and effective lipid-lowering therapeutic agents.

Dietary flavonoids: effects on endothelial function and blood pressure

Several population studies have found an inverse association between flavonoid intake and risk of cardiovascular disease. These studies have resulted in the hypothesis that dietary flavonoids protect against cardiovascular disease. Many in vitro studies, studies using animal models and human intervention trials have been carried out to investigate how flavonoids might provide protection. Emerging and largely consistent evidence suggests that flavonoids can improve endothelial function and may reduce blood pressure. In vitro studies show that a variety of flavonoids cause vasorelaxation of isolated arteries from rats. In human intervention trials, flavonoids derived from tea and cocoa or dark chocolate—both rich sources of catechins—have been found to improve endothelial function acutely and with regular ingestion. The evidence for benefits of flavonoids from other dietary sources is less clear. Improvements in endothelial function could contribute to lower blood pressure. Population studies have associated higher intake of tea and chocolate with lower blood pressure. Short‐term intervention studies in humans have shown blood pressure lowering with cocoa or dark chocolate, but short‐term regular ingestion of tea has not been found to lower blood pressure. The long‐term effects of regular ingestion of a flavonoid‐enriched diet on endothelial function and blood pressure have yet to be assessed. In addition, there is evidence that flavonoid metabolism is an important factor influencing the biological activity and effects of dietary flavonoids, but further studies are needed to investigate this area. Copyright © 2006 Society of Chemical Industry

Epigallocatechin gallate and caffeine differentially inhibit the intestinal absorption of cholesterol and fat in ovariectomized rats

We conducted this study to determine whether green tea constituents, (-)-epigallocatechin gallate (EGCG) and caffeine, affect the intestinal absorption of cholesterol (CH), fat, and other fat-soluble compounds. Ovariectomized rats with lymph cannula were infused intraduodenally with a lipid emulsion containing 14C-labeled CH (14C-CH), alpha-tocopherol (alpha TOH), triolein, and sodium taurocholate, without (control) or with EGCG, caffeine, or EGCG plus caffeine, in PBS, pH 6.5. The lymphatic total 14C-CH was significantly lowered by EGCG (21.1 +/- 2.1% dose), caffeine (27.9 +/- 1.7% dose), and EGCG plus caffeine (19.3 +/- 0.9% dose), compared with the control (32.4 +/- 1.6% dose). The lymphatic output of esterified CH also was significantly lower in rats infused with EGCG (7.9 +/- 0.7 micromol), caffeine (7.6 +/- 0.2 micromol), and EGCG plus caffeine (7.5 +/- 0.6 micromol) than rats in the control group (11.6 +/- 1.7 micromol). Also, EGCG and caffeine significantly lowered the absorption of alpha TOH, another highly hydrophobic lipid. However, the lymphatic outputs of oleic acid (exogenous fatty acid marker) and other fatty acids of endogenous origin were not affected by EGCG but were markedly lowered by caffeine and EGCG plus caffeine. Caffeine significantly lowered the amount of lymph flow, regardless of whether it was infused alone (14.2 +/- 3.9 mL) or with EGCG (18.6 +/- 2.0 mL), compared with EGCG (22.2 +/- 2.2 mL) alone and the control group (23.2 +/- 3.8 mL). The caffeine-induced decline in lymph flow was associated with the lowering of lipid absorption. The results indicate that both EGCG and caffeine inhibit lipid absorption and that the inhibitory effects of the 2 tea constituents are not synergistic but mediated by distinctly different mechanisms.

Fruit and vegetable juices and Alzheimer's disease: the Kame Project

BACKGROUND

Growing evidence suggests that oxidative damage caused by the beta-amyloid peptide in the pathogenesis of Alzheimer's disease may be hydrogen peroxide mediated. Many polyphenols, the most abundant dietary antioxidants, possess stronger neuroprotection against hydrogen peroxide than antioxidant vitamins.

METHODS

We tested whether consumption of fruit and vegetable juices, containing a high concentration of polyphenols, decreases the risk of incident probable Alzheimer's disease in the Kame Project cohort, a population-based prospective study of 1836 Japanese Americans in King County, Washington, who were dementia-free at baseline (1992-1994) and were followed through 2001.

RESULTS

After adjustment for potential confounders, the hazard ratio for probable Alzheimer's disease was 0.24 (95% confidence interval [CI], 0.09-0.61) comparing subjects who drank juices at least 3 times per week with those who drank less often than once per week with a hazard ratio of 0.84 (95% CI, 0.31-2.29) for those drinking juices 1 to 2 times per week (P for trend < .01). This inverse association tended to be more pronounced among those with an apolipoprotein Eepsilon-4 allele and those who were not physically active. Conversely, no association was observed for dietary intake of vitamins E, C, or beta-carotene or tea consumption.

CONCLUSIONS

Fruit and vegetable juices may play an important role in delaying the onset of Alzheimer's disease, particularly among those who are at high risk for the disease. These results may lead to a new avenue of inquiry in the prevention of Alzheimer's disease.

Acute Effect of Black and Green Tea on Aortic Stiffness and Wave Reflections

OBJECTIVE

While most studies have shown an inverse relation between tea consumption and cardiovascular risk, other studies have shown opposite results. Aortic stiffness and wave reflections are markers of cardiovascular disease and prognosticators of cardiovascular risk.

METHODS

The acute effect of black and green tea on aortic stiffness and wave reflections was assessed in 29 healthy volunteers in a randomized, single-blind, sham-procedure controlled, cross-over design. In the black tea sub-study, 16 subjects received 6 gm of tea, caffeine (175 mg), or hot water in 3 different sessions. In the green tea sub-study, 13 subjects received 6 gm of tea, caffeine (125 mg), or hot water. Carotid-femoral pulse wave velocity and wave reflection indices were measured at baseline and for 3 hours after consumption.

RESULTS

Black tea increased pulse wave velocity during the first 90 min (increase by 0.49 m/sec, P < 0.05), showing a rapid return towards baseline values thereafter (P = 0.07 for the whole study period); in contrast, green tea had no effect. Both black and green tea increased augmentation index (by 5.0% and by 6.6%, P < 0.01 and P < 0.001, respectively) throughout the study. These changes were less than the respective changes produced by caffeine. Both black and green tea had a significant pressor effect. No change in oxidant status was found with both types of tea.

CONCLUSIONS

Both black and green tea increases acutely wave reflections and only black tea increases aortic stiffness. Tea flavonoids may play a role in the attenuation of the effects of caffeine contained in tea.

Consumo de Camellia sinensis em população de origem oriental e incidência de doenças crônicas

Investigar os prováveis benefícios dos hábitos culturais orientais, incluindo o consumo de Camellia sinensis (chá verde) na prevenção de doenças crônicas. Trinta e quatro indivíduos entre 25 e 84 anos, de ambos os sexos, pertencentes à comunidade nipônica do Rio de Janeiro, RJ, foram submetidos a anamnese alimentar e questionário socio-econômico-cultural. Dos indivíduos, 76% consumiam chá verde, sendo que 35% o ingeriam diariamente e 27% esporadicamente. Verificou-se que o consumo regular de álcool era predominante nos não usuários de chá verde, quando comparados com os apreciadores da bebida (50% e 35%, respectivamente, faziam uso de álcool). Não foi observado sedentarismo na amostra. Dos apreciadores do chá, 81% não apresentavam doenças crônicas. Já entre os consumidores, observamos um menor percentual de doenças crônicas, especialmente, de hipertensão, porém sem significância estatística.

Green Tea Consumption and Serum Malondialdehyde-Modified LDL Concentrations in Healthy Subjects

OBJECTIVE

Green tea was shown to inhibit LDL oxidation, platelet aggregation, and matrix metalloproteinases (MMPs) activities in vitro. We tried to elucidate whether or not green tea consumption may have these effects in vivo, which may be protective against atherosclerotic disease.

METHODS

We measured serum malondialdehyde-modified LDL (MDA-LDL) concentrations and urine 8-epi-prostaglandin (PG) F(2alpha) in 22 healthy male nonsmokers. They drank 7 cups/day of water for 2 weeks and drank 7 cups/day of green tea for the next 2 weeks. Regarding platelet aggregation, plasma thromboxane B(2) (TXB(2)) and 6-keto-PGF(1alpha) concentrations and ex vivo platelet aggregation were evaluated. Plasma MMP-2 and -9 concentrations were also measured.

RESULTS

Of the 22 subjects, 20 had been in the habit of drinking green tea before the study. Plasma catechins concentrations significantly decreased at the end of the water period and then increased at the end of the green tea period. Although no change in plasma LDL-cholesterol concentrations (110 +/- 33 vs. 113 +/- 28 mg/dL, p = NS) was found, MDA-LDL concentrations (84 +/- 45 vs. 76 +/- 40 IU/L, p < 0.05) and the ratio of MDA-LDL/LDL-cholesterol (0.74 +/- 0.21 vs. 0.65 +/- 0.20, p < 0.02) significantly decreased at the end of the green tea period. However, no significant changes were observed in urine 8-epi-PGF(2alpha) concentrations, in platelet aggregation, nor in plasma TXB(2), 6-keto-PGF(1alpha) or MMP concentrations.

CONCLUSION

Daily consumption of green tea decreased serum MDA-LDL concentrations, but it had no significant effects on platelet aggregation, platelet TX production or plasma MMPs concentrations. Our results suggest that green tea consumption may inhibit LDL oxidation in vivo.

Oral administration of a decaffeinated green tea (Camellia sinensis) extract did not alter urinary 8-epi-prostaglandin F(2 alpha), a biomarker for in-vivo lipid peroxidation

Oxidative stress is involved in the pathogenesis of numerous chronic human diseases. The objective of this study was to determine whether administration of a decaffeinated green tea extract providing 844 mg flavonoids daily reduced the urinary excretion of 8-epi-prostaglandin F(2 alpha) (8-epi-PGF(2 alpha)), a product of lipid peroxidation in cellular membranes and of low-density lipoprotein (LDL). Nine healthy male and female subjects were studied at baseline and after 14 days of green tea supplementation. Analysis of urinary 8-epi-PGF(2 alpha) was performed using immunoaffinity extraction-gas chromatography-negative ion chemical ionization-mass spectrometry (GC-NICI-MS). Urinary 8-epi-PGF(2 alpha) concentrations were 0.286+/-0.120 nmol (mmol creatinine)(-1) at baseline and 0.244+/-0.177 nmol mmol(-1) creatinine after green tea supplementation. There were no significant differences in the excretion of urinary 8-epi-PGF(2 alpha) after treatment with green tea. We conclude that 14 days of green tea supplementation did not significantly alter in-vivo lipid peroxidation.

Addition of milk does not alter the antioxidant activity of black tea

Tea is a polyphenol-rich beverage like wine and catechins are its chief polyphenols. Catechins have cardio-protective effects as they can scavenge free radicals and inhibit lipid peroxidation. Epidemiological studies indicate an inverse relation between tea consumption and the risk of cardiovascular and other chronic diseases. Addition of milk to black tea has been reported to adversely affect its beneficial effects, but the data are not unequivocal. Therefore, we assessed the effect of the addition of milk to black tea on its ability to modulate oxidative stress and antioxidant status in adult male human volunteers. Although the area under the curve of plasma catechins was lower on the consumption of tea with milk compared to black tea, it did not affect the beneficial effects of black tea on total plasma antioxidant activity, plasma resistance to oxidation induced ex vivo, and decreased plasma and urinary thiobarbituric acid reactive substance levels. The results suggest that addition of milk may not obviate the ability of black tea to modulate the antioxidant status of subjects and that consumption of black tea with/without milk prevents oxidative damage in vivo.

The combination of vitamin C and grape-seed polyphenols increases blood pressure: a randomized, double-blind, placebo-controlled trial

BACKGROUND

There is growing evidence that oxidative stress contributes to the pathogenesis of hypertension and endothelial dysfunction. Thus, dietary antioxidants may beneficially influence blood pressure (BP) and endothelial function by reducing oxidative stress.

OBJECTIVE

To determine if vitamin C and polyphenols, alone or in combination, can lower BP, improve endothelial function and reduce oxidative stress in hypertensive individuals.

DESIGN

A total of 69 treated hypertensive individuals with a mean 24-h ambulatory systolic blood pressure > or = 125 mmHg participated in a randomized, double-blind, placebo-controlled, factorial trial. Following a 3-week washout, participants received 500 mg/day vitamin C, 1000 mg/day grape-seed polyphenols, both vitamin C and polyphenols, or neither for 6 weeks. At baseline and post-intervention, 24-h ambulatory BP, ultrasound-assessed endothelium-dependent and -independent vasodilation of the brachial artery, and markers of oxidative damage, (plasma and urinary F2-isoprostanes, oxidized low-density lipoproteins and plasma tocopherols), were measured.

RESULTS

A significant interaction between grape-seed and vitamin C treatments for effects on BP was observed. Vitamin C alone reduced systolic BP versus placebo (-1.8 +/- 0.8 mmHg, P = 0.03), while polyphenols did not (-1.3 +/- 0.8 mmHg, P = 0.12). However, treatment with the combination of vitamin C and polyphenols increased systolic BP (4.8 +/- 0.9 mmHg versus placebo; 6.6 +/- 0.8 mmHg versus vitamin C; 6.1 +/- 0.9 mmHg versus polyphenols mmHg, each P < 0.0001) and diastolic BP (2.7 +/- 0.6 mmHg, P < 0.0001 versus placebo; 1.5 +/- 0.6 mmHg, P = 0.016 versus vitamin C; 3.2 +/- 0.7 mmHg, P < 0.0001 versus polyphenols). Endothelium-dependent and -independent vasodilation, and markers of oxidative damage were not significantly altered.

CONCLUSION

Although the mechanism remains to be elucidated, these results suggest caution for hypertensive subjects taking supplements containing combinations of vitamin C and polyphenols.

The effects of coffee consumption on lipid peroxidation and plasma total homocysteine concentrations: a clinical trial

Despite extensive research, the cardiovascular effects of coffee consumption in humans remain controversial. Our aim was to investigate the excretion of coffee phenols and the effects of filtered coffee consumption on oxidative stress and plasma homocysteine (tHcy) concentration in humans. The study consisted of a multiple-dose clinical supplementation trial and a single-dose study. In the long-term trial, 43 healthy nonsmoking men optionally consumed daily either no coffee, 3 cups (450 mL), or 6 cups (900 mL) of filtered coffee for 3 weeks, while in the short-term study 35 subjects consumed a single dose of 0, 1 (150 mL), or 2 cups (300 mL) of coffee. Long-term consumption of coffee increased the urinary excretion of caffeic and ferulic acid. The change in the total excretion of phenolic acids in 3 and 6 cups groups represented 3.8 and 2.5% of the amount ingested daily. Plasma tHcy concentrations increased nonsignificantly, but the consumption of coffee had neither short-nor long-term effects on lipid peroxidation or the activity of measured antioxidant enzymes. In conclusion, the consumption of filtered coffee does not have any detectable effects on lipid peroxidation in healthy nonsmoking men. The effect of coffee consumption on tHcy concentrations needs further investigation.

Polyphenols and prevention of cardiovascular diseases

PURPOSE OF REVIEW

Polyphenols are the most abundant dietary antioxidants and research on their role in the prevention of degenerative diseases has developed quickly over these last few years. This paper reviews the recent studies on the prevention of cardiovascular diseases by polyphenols, focusing on human studies.

RECENT FINDINGS

A large number of recent intervention studies have shown that several biomarkers of cardiovascular risk are influenced by the consumption of polyphenol-rich foods. Effects on biomarkers of oxidative stress, lipemia and inflammation appear so far inconclusive. More consistent effects have been observed on endothelial function and haemostasis and support a reduction of risk by polyphenols in agreement with the few epidemiological studies already published. All clinical studies have used foods or beverages containing a mixture of different polyphenols and the exact nature of the most active compounds remains largely unknown. Absorption, metabolism and elimination vary widely between polyphenols. These data on bioavailability should be taken into account to improve the experimental design and the interpretation of the observed effects.

SUMMARY

Future intervention studies should include a detailed assessment of the bioavailability of polyphenols. Beyond clinical trials carried out with polyphenol-rich foods, more studies with pure polyphenols will also be needed to establish their role in the prevention of cardiovascular diseases.

Health promotion by flavonoids, tocopherols, tocotrienols, and other phenols: direct or indirect effects? Antioxidant or not?

Foods and beverages rich in phenolic compounds, especially flavonoids, have often been associated with decreased risk of developing several diseases. However, it remains unclear whether this protective effect is attributable to the phenols or to other agents in the diet. Alleged health-promoting effects of flavonoids are usually attributed to their powerful antioxidant activities, but evidence for in vivo antioxidant effects of flavonoids is confusing and equivocal. This may be because maximal plasma concentrations, even after extensive flavonoid intake, may be low (insufficient to exert significant systemic antioxidant effects) and because flavonoid metabolites tend to have decreased antioxidant activity. Reports of substantial increases in plasma total antioxidant activity after flavonoid intake must be interpreted with caution; findings may be attributable to changes in urate concentrations. However, phenols might exert direct effects within the gastrointestinal tract, because of the high concentrations present. These effects could include binding of prooxidant iron, scavenging of reactive nitrogen, chlorine, and oxygen species, and perhaps inhibition of cyclooxygenases and lipoxygenases. Our measurements of flavonoids and other phenols in human fecal water are consistent with this concept. We argue that tocopherols and tocotrienols may also exert direct beneficial effects in the gastrointestinal tract and that their return to the gastrointestinal tract by the liver through the bile may be physiologically advantageous.

Factors regulating isoprostane formation in vivo

Discovery of the F2-isoprostanes, a group of prostaglandin F2-like compounds biosynthesized from arachidonic acid nonenzymatically, has uncovered a new and novel facet of free radical biology. Some of these compounds are bioactive and thus may mediate adverse effects associated with oxidant stress. F2-Isoprostanes have also been shown to be reliable biomarkers of lipid peroxidation. Factors influencing their formation and metabolism have been studied to some extent, although much remains to be determined. The purpose of this review is to summarize our current knowledge of conditions that modulate endogenous generation of these compounds. Isoprostanes have a wide daily variation in secretion in humans. Although normal levels can be defined, these compounds are found in increased concentrations in various pathophysiological states, including ischemia-reperfusion injury, atherosclerosis, and diabetes, and in experimental conditions of oxidative stress and inflammation. Alterations in isoprostane biosynthesis, secretion, and excretion in normal physiology and in pathophysiological states are due to the various types of endogenous and exogenous regulatory mechanisms that control the availability of precursors required for isoprostane synthesis, such as dietary and tissue arachidonic acid content, oxygen concentration, and the generation of various free radical species. Selected aspects of issues related to isoprostane formation and metabolism in vivo will be examined herein.

Bioavailability and bioefficacy of polyphenols in humans. II. Review of 93 intervention studies

For some classes of dietary polyphenols, there are now sufficient intervention studies to indicate the type and magnitude of effects among humans in vivo, on the basis of short-term changes in biomarkers. Isoflavones (genistein and daidzein, found in soy) have significant effects on bone health among postmenopausal women, together with some weak hormonal effects. Monomeric catechins (found at especially high concentrations in tea) have effects on plasma antioxidant biomarkers and energy metabolism. Procyanidins (oligomeric catechins found at high concentrations in red wine, grapes, cocoa, cranberries, apples, and some supplements such as Pycnogenol) have pronounced effects on the vascular system, including but not limited to plasma antioxidant activity. Quercetin (the main representative of the flavonol class, found at high concentrations in onions, apples, red wine, broccoli, tea, and Ginkgo biloba) influences some carcinogenesis markers and has small effects on plasma antioxidant biomarkers in vivo, although some studies failed to find this effect. Compared with the effects of polyphenols in vitro, the effects in vivo, although significant, are more limited. The reasons for this are 1) lack of validated in vivo biomarkers, especially in the area of carcinogenesis; 2) lack of long-term studies; and 3) lack of understanding or consideration of bioavailability in the in vitro studies, which are subsequently used for the design of in vivo experiments. It is time to rethink the design of in vitro and in vivo studies, so that these issues are carefully considered. The length of human intervention studies should be increased, to more closely reflect the long-term dietary consumption of polyphenols.

Bioavailability and antioxidant activity of tea flavanols after consumption of green tea, black tea, or a green tea extract supplement

BACKGROUND

Green and black tea polyphenols have been extensively studied as cancer chemopreventive agents. Many in vitro experiments have supported their strong antioxidant activity. Additional in vivo studies are needed to examine the pharmacokinetic relation of absorption and antioxidant activity of tea polyphenols administered in the form of green or black tea or tea extract supplements.

OBJECTIVE

The purpose of this study was to compare the pharmacokinetic disposition of tea polyphenols and their effect on the antioxidant capacity in plasma 8 h after a bolus consumption of either green tea, black tea, or a green tea extract supplement.

DESIGN

Thirty healthy subjects were randomly assigned to 3 different sequences of green tea, black tea, or a green tea extract supplement in a 3 x 3 crossover design with a 1-wk washout period in between treatments.

RESULTS

Flavanol absorption was enhanced when tea polyphenols were administered as a green tea supplement in capsule form and led to a small but significant increase in plasma antioxidant activity compared with when tea polyphenols were consumed as black tea or green tea. All 3 interventions provided similar amounts of (-)-epigallocatechin-3-gallate.

CONCLUSIONS

Our observations suggest that green tea extract supplements retain the beneficial effects of green and black tea and may be used in future chemoprevention studies to provide a large dose of tea polyphenols without the side effects of caffeine associated with green and black tea beverages.

Flavanol-rich cocoa drink lowers plasma F(2)-isoprostane concentrations in humans

Flavan-3-ols are potent antioxidants in vitro, but convincing evidence for antioxidant action in vivo is lacking. We examined whether an oxidative stress-mediated increase in plasma F(2)-isoprostanes is counteracted by a flavanol-rich cocoa beverage. Twenty volunteers were examined in a comparative randomized double-blind crossover design with respect to ingestion of high-flavanol cocoa drink (HFCD; 187 mg flavan-3-ols/100 ml) vs. low-flavanol cocoa drink (LFCD; 14 mg/100 ml). With 10 individuals, the treatment was combined with strenuous physical exercise. Total (esterified plus nonesterified) F(2)-isoprostanes were analyzed by GC/MS. LFCD caused a slight increase in the mean (+/- SEM) plasma concentrations of F(2)-isoprostanes 2 and 4 h after intake (2.16 +/- 0.19 nM at 4 h vs. 1.76 +/- 0.11 nM at 0 h, n = 10), which may be attributable to postprandial oxidative stress. This increase did not occur with HFCD (1.57 +/- 0.06 nM at 4 h vs. 1.65 +/- 0.10 nM at 0 h, n = 10). The difference in F(2)-isoprostanes 2 and 4 h after intake of HFCD vs. LFCD became statistically significant when the intake was combined with physical exercise (P < 0.01, ANOVA). We conclude that dietary flavanols, using cocoa drink as example, can lower the plasma level of F(2)-isoprostanes, indicators of in vivo lipid peroxidation.

The 6-a-day study: effects of fruit and vegetables on markers of oxidative stress and antioxidative defense in healthy nonsmokers

BACKGROUND

Fruit and vegetables contain both nutritive and nonnutritive factors that might contribute to redox (antioxidant and prooxidant) actions.

OBJECTIVE

We investigated the relative influence of nutritive and nonnutritive factors in fruit and vegetables on oxidative damage and enzymatic defense.

DESIGN

A 25-d intervention study with complete control of dietary intake was performed in 43 healthy male and female nonsmokers who were randomly assigned to 1 of 3 groups. In addition to a basic diet devoid of fruit and vegetables, the fruit and vegetables (Fruveg) group received 600 g fruit and vegetables/d; the placebo group received a placebo pill, and the supplement group received a vitamin pill designed to contain vitamins and minerals corresponding to those in 600 g fruit and vegetables. Biomarkers of oxidative damage to protein and lipids and of antioxidant nutrients and defense enzymes were determined before and during intervention.

RESULTS

Plasma lipid oxidation lag times increased during intervention in the Fruveg and supplement groups, and the increase was significantly higher in the former. Plasma protein carbonyl formation at lysine residues also increased in both of these groups. Glutathione peroxidase activity increased in the Fruveg group only. Other markers of oxidative damage, oxidative capacity, or antioxidant defense were largely unaffected by the intervention.

CONCLUSIONS

Fruit and vegetables increase erythrocyte glutathione peroxidase activity and resistance of plasma lipoproteins to oxidation more efficiently than do the vitamins and minerals that fruit and vegetables are known to contain. Plasma protein carbonyl formation at lysine residues increases because of the vitamins and minerals in fruit and vegetables.

Phenolic acid metabolites as biomarkers for tea- and coffee-derived polyphenol exposure in human subjects

Tea and coffee are rich in polyphenols with a variety of biological activities. Many of the demonstrated activities are consistent with favourable effects on the risk of chronic diseases. 4-O-methylgallic acid (4OMGA) and isoferulic acid are potential biomarkers of exposure to polyphenols derived from tea and coffee respectively. 4OMGA is derived from gallic acid in tea, and isoferulic acid is derived from chlorogenic acid in coffee. Our major objective was to explore the relationships of tea and coffee intake with 24 h urinary excretion of 4OMGA and isoferulic acid in human subjects. The relationships of long-term usual (111 participants) and contemporaneously recorded current (344 participants) tea and coffee intake with 24 h urinary excretion of 4OMGA and isoferulic acid were assessed in two populations. 4OMGA was related to usual (r 0.50, P<0.001) and current (r 0.57, P<0.001) tea intake, and isoferulic acid was related to usual (r 0.26, P=0.008) and current (r 0.18, P<0.001) coffee intake. Overall, our present results are consistent with the proposal that 4OMGA is a good biomarker for black tea-derived polyphenol exposure, but isoferulic acid may be of limited usefulness as a biomarker for coffee-derived polyphenol exposure.