Black tea increases the resistance of human plasma to lipid peroxidation in vitro, but not ex vivo

In vivo effects of black tea on the male rat reproductive system and functions of the kidney and liver

This study focused on the effects of black tea on the male reproductive system as well as the kidney and liver functions. Male Wistar rats were given aqueous extract of black tea (2% and 5%) for 52 days as the only means of drinking fluid, while control rats received tap water. Black tea enhanced sperm vitality (44%-49%), total sperm motility (10%-12%) and acrosome reaction (2%-9%) (p < .05). Body weight gain, testis, epididymis, seminal vesicles, prostate, liver weight, testosterone level, sperm concentration, ferric reducing antioxidant power (FRAP) and antioxidant levels in the testes, liver and kidney remained unchanged (p > .05). Black tea (5%) increased kidney weight (p < .05). Testis and epididymis showed normal histological appearance. However, black tea significantly reduced the diameter (9%-10%) and epithelial height (9%-10%) of the seminiferous tubule, but increased the epithelial height of the cauda epididymis (8%-24%) (p < .05). A significant reduction in serum levels of alanine aminotransaminase (ALT) (38%) and aspartate aminotransaminase (AST) (23%-34%) was observed (p < .05); creatinine level, on the other hand, increased (8%-72%) (p < .05). Black tea improved several sperm parameters, but may cause subtle changes in certain reproductive organs and the kidney functions.

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

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

The impact of supplementation with pomegranate fruit (Punica granatum L.) juice on selected antioxidant parameters and markers of iron metabolism in rowers

Background

The aim of this study was to analyse the effect of pomegranate juice (POM) supplementation on the levels of selected pro-inflammatory cytokines, hepcidin and markers of iron metabolism in well-trained rowers.

Method

The double-blind placebo-controlled study included 19 members of the Polish Rowing Team. The athletes were randomised into the supplemented group (n = 10), receiving 50 ml of standardised POM daily for two months, or the placebo group (n = 9). The subjects performed a 2000 m test on the rowing ergometer at the start of the project (baseline) and end of follow-up period. Blood samples from the antecubital vein were obtained three times during each trial: prior to the exercise, one minute after the test, and following a 24 h recovery.

Results

The study documented the beneficial effect of supplementation with pomegranate fruit juice on TAC (P < 0.002). During the resting period, TAC level in the supplemented group was significantly higher than in the placebo group (x ± SD, 2.49 ± 0.39 vs. 1.88 ± 0.45, P < 0.05). The ergometric test conducted at baseline demonstrated a significant post-exercise increase in the concentrations of soluble transferrin receptors (P < 0.04), iron (P < 0.002) and IL-6 (P < 0.02), and to a significant post-exercise decrease in TAC. A significant increase in IL-6 concentration was also observed 24 h post-exercise. The exercise test conducted at the end of the follow-up period resulted in a significant decrease in TBIC and a significant increase in UIBC (P < 0.001), observed in both groups, both immediately post-exercise and after the resting period.

Conclusion

Supplementation with POM contributed to a significant strengthening of plasma antioxidant potential in the group of well-trained rowers, but had no effect on iron metabolism markers.

Overexpression of glutathione peroxidase 1 predicts poor prognosis in oral squamous cell carcinoma

PURPOSE

Intracellular antioxidant enzymes are commonly upregulated in various cancer types and are associated with treatment outcomes. Because the relationship has rarely been examined in oral squamous cell carcinoma (OSCC), we aimed to evaluate the association between the levels of glutathione peroxidase (GPX)1, GPX4, and thioredoxin reductase (TrxR)1 expression and prognosis in patients with OSCC who underwent curative surgical resection.

METHODS

This study included 233 patients who underwent curative surgery for previously untreated OSCC between 2000 and 2012. Tumour GPX1, GPX4, and TrxR1 expression was evaluated by immunohistochemistry and was dichotomised to low and high values according to defined expression levels. The association between GPX1, GPX4, and TrxR1 expression and clinicopathological results was analysed. Univariate and multivariate analyses using the Cox proportional hazards model were conducted to assess the significance of differences in recurrence or survival outcomes between variables.

RESULTS

High GPX1, GPX4, and TrxR1 expression was observed in 99 (42.5%), 133 (57.1%), and 46 (19.7%) patients, respectively. GPX1 overexpression was significantly correlated with nodal metastasis, advanced overall stage, depth of invasion of >10 mm, high grade and perineural invasion (P < 0.05). High GPX4 expression was also related to nodal metastasis, overall advanced stage and high grade (P < 0.05). Univariate and multivariate analyses showed that increased GPX1 expression was significantly associated with poor disease-free, cancer-specific and overall survival (all P < 0.05), while increased GPX4 or TrxR1 expression was not (all P > 0.1).

CONCLUSIONS

Tumour GPX1 expression is a useful biomarker predictive of recurrence and survival in OSCC patients.

Dietary Phytochemicals Promote Health by Enhancing Antioxidant Defence in a Pig Model

Phytochemical-rich diets are protective against chronic diseases and mediate their protective effect by regulation of oxidative stress (OS). However, it is proposed that under some circumstances, phytochemicals can promote production of reactive oxygen species (ROS) in vitro, which might drive OS-mediated signalling. Here, we investigated the effects of administering single doses of extracts of red cabbage and grape skin to pigs. Blood samples taken at baseline and 30 min intervals for 4 hours following intake were analyzed by measures of antioxidant status in plasma, including Trolox equivalent antioxidant capacity (TEAC) and glutathione peroxidase (GPx) activity. In addition, dose-dependent production of hydrogen peroxide (H₂O₂) by the same extracts was measured in untreated commercial pig plasma in vitro. Plasma from treated pigs showed extract dose-dependent increases in non-enzymatic (plasma TEAC) and enzymatic (GPx) antioxidant capacities. Similarly, extract dose-dependent increases in H₂O₂ were observed in commercial pig plasma in vitro. The antioxidant responses to extracts by treated pigs were highly correlated with their respective yields of H₂O₂ production in vitro. These results support that dietary phytochemicals regulate OS via direct and indirect antioxidant mechanisms. The latter may be attributed to the ability to produce H₂O₂ and to thereby stimulate cellular antioxidant defence systems.

Reactive oxygen species and cancer paradox: To promote or to suppress?

Reactive oxygen species (ROS), a group of highly reactive ions and molecules, are increasingly being appreciated as powerful signaling molecules involved in the regulation of a variety of biological processes. Indeed, their role is continuously being delineated in a variety of pathophysiological conditions. For instance, cancer cells are shown to have increased ROS levels in comparison to their normal counterparts. This is partly due to an enhanced metabolism and mitochondrial dysfunction in cancer cells. The escalated ROS generation in cancer cells contributes to the biochemical and molecular changes necessary for the tumor initiation, promotion and progression, as well as, tumor resistance to chemotherapy. Therefore, increased ROS in cancer cells may provide a unique opportunity to eliminate cancer cells via elevating ROS to highly toxic levels intracellularly, thereby, activating various ROS-induced cell death pathways, or inhibiting cancer cell resistance to chemotherapy. Such results can be achieved by using agents that either increase ROS generation, or inhibit antioxidant defense, or even a combination of both. In fact, a large variety of anticancer drugs, and some of those currently under clinical trials, effectively kill cancer cells and overcome drug resistance via enhancing ROS generation and/or impeding the antioxidant defense mechanism. This review focuses on our current understanding of the tumor promoting (tumorigenesis, angiogenesis, invasion and metastasis, and chemoresistance) and the tumor suppressive (apoptosis, autophagy, and necroptosis) functions of ROS, and highlights the potential mechanism(s) involved. It also sheds light on a very novel and an actively growing field of ROS-dependent cell death mechanism referred to as ferroptosis.

Effects of cranberry (Vaccinum macrocarpon) supplementation on iron status and inflammatory markers in rowers

Background

The aim of this study was to analyze the effect of supplementation with cranberry (Vaccinum macrocarpon) on the levels of pro-inflammatory cytokines, hepcidin and selected markers of iron metabolism in rowers subjected to exhaustive exercise.

Methods

This double-blind study included 16 members of the Polish Rowing Team. The subjects were randomly assigned to the supplemented group (n = 9), receiving 1200 mg of cranberry extract for 6 weeks, or to the placebo group (n = 7). The participants performed a 2000-m test on a rowing ergometer at the beginning and at the end of the preparatory camp. Blood samples were obtained from the antecubital vein prior to each exercise test, one minute after completing the test, and after a 24-h recovery period. The levels of hepcidin, interleukin 6 (IL-6), tumor necrosis factor alpha (TNF-alpha), ferritin, iron, soluble transferrin receptor (sTfR) and myoglobin were determined, along with total iron-binding capacity (TIBC), unbound iron-binding capacity (UIBC) and total antioxidant capacity (TAC).

Results

Both prior and after the supplementation, a significant post-exercise increase in the concentration of IL-6 was observed in both groups. At the end of the study period, cranberry-supplemented athletes presented with significantly higher resting, post-exercise and post-recovery levels of TAC than the controls. However, a significant exercise-induced increase in the concentrations of TNF-alpha, myoglobin and hepcidin was observed solely in the control group.

Conclusion

Supplementation with cranberry extract contributed to a significant strengthening of antioxidant potential in individuals exposed to strenuous physical exercise. However, supplementation did not exert direct effects on other analyzed parameters: inflammatory markers and indices of iron metabolism (TNF-alpha, hepcidin and myoglobin).

Dietary intake of natural antioxidants: vitamins and polyphenols

Oxidative stress is a condition in which oxidant metabolites exert their toxic effect because of an increased production or an altered cellular mechanism of protection; oxidative stress is rapidly gaining recognition as a key phenomenon in chronic diseases. Antioxidants terminate these chain reactions by removing free radical intermediates, and inhibit other oxidation reactions by being oxidized themselves. Endogenous defence mechanisms are inadequate for the complete prevention of oxidative damage, and different sources of dietary antioxidants may be especially important. This article calls attention to the dietary antioxidants, such as vitamins A, C, and E and polyphenols. Compelling evidence has led to the conclusion that diet is a key environmental factor and a potential tool for the control of chronic diseases. More specifically, fruits and vegetables have been shown to exert a protective effect. The high content of minerals and natural antioxidant as vitamins A, C, and E and polyphenols in fruits and vegetables may be a main factor responsible for these effects.

Bioavailability of Plant-Derived Antioxidants

Natural products with antioxidant properties have been extensively utilized in the pharmaceutical and food industry and have also been very popular as health-promoting herbal products. This review provides a summary of the literature published around the first decade of the 21st century regarding the oral bioavailability of carotenoids, polyphenols and sulfur compounds as the three major classes of plant-derived antioxidants. The reviewed original research includes more than 40 compounds belonging to the above mentioned classes of natural antioxidants. In addition, related reviews published during the same period have been cited. A brief introduction to general bioavailability-related definitions, procedures and considerations is also included.

Polyphenol compounds in the chicken/animal diet: from the past to the future

Animal feed provides a range of antioxidants that help the body building an integrated antioxidant system responsible for a prevention of damaging effects of free radicals and products of their metabolism. Vitamin E is considered to be the main chain-breaking antioxidant located in the membranes and effectively protecting them against lipid peroxidation. Recently, various polyphenol compounds, especially flavonoids, have received substantial attention because of their antioxidant activities in various in vitro systems. However, it was shown that flavonoid compounds are poorly absorbed in the gut and their concentrations in target tissues are too low to perform an effective antioxidant defences. The aim of the present paper is to review existing evidence about possible roles of various plant extracts provided with the diet in animal/poultry nutrition with a specific emphasis to their antioxidant activities.

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.

The antioxidant effects of a polyphenol-rich grape pomace extract in vitro do not correspond in vivo using exercise as an oxidant stimulus

Fruits, such as grapes, are essential food of the Mediterranean diet. Grape extracts have potent antioxidant and chemopreventive properties in vitro. Numerous studies have examined the effects of plant extract administration on redox status at rest in animals and humans but their results are controversial. However, there are no studies comparing the in vitro and in vivo effects of plant extracts on oxidative stress using exercise as an oxidant stimulus. Thus, the aim of this study was to investigate whether a polyphenol-rich grape pomace extract of the Vitis vinifera species possesses in vitro antioxidant properties and to examine whether these properties apply in an in vivo model at rest and during exercise. Our findings indicate that the tested extract exhibits potent in vitro antioxidant properties because it scavenges the DPPH(•) and ABTS(•+) radicals and inhibits DNA damage induced by peroxyl and hydroxyl radicals. Administration of the extract in rats generally induced oxidative stress at rest and after exercise whereas exercise performance was not affected. Our findings suggest that the grape pomace extract does not behave with the same way in vitro and in vivo.

Dietary oxidative stress and antioxidant defense with an emphasis on plant extract administration

Eukaryotic cells generally function in a reduced state, but an amount of reactive species is essential for several biochemical processes. The antioxidant network is the defensive mechanism that occurs when the concentration of reactive species exceeds a threshold. Polyphenolic compounds present in plant extracts are potent antioxidants in vitro, but they may promote oxidative stress when administered in animals and humans, especially when given as supplements in exercise, a modality usually adopted as an oxidant stimulus. This is mainly observed when antioxidant molecules are administered separately and not as part of a diet. Exercise is usually adopted as a physiological model for examining the effects of reactive species in human or animal physiology. The use of exercise as a model demonstrates that reactive species do not always have adverse effects, but are necessary in physiological processes that are beneficial for human health. This review summarizes what is known about antioxidant supplementation and demonstrates the need for a meticulous examination of the in vitro findings before applying them to in vivo models. The term "antioxidant" seems elusive, and it is more appropriate to characterize a compound as "antioxidant" if we know in which concentration it is used, when it is used, and under which conditions.

Tea and cardiovascular disease

There is increasing evidence for a protective effect of tea consumption against cardiovascular disease. This review summarizes the available epidemiological data providing evidence for and against such an effect. We also review observational and intervention studies that investigated an effect of tea and tea extracts on cardiovascular risk factors, including blood pressure, serum lipids, diabetes mellitus, and obesity. Finally, we review potential mechanisms of benefit, including anti-inflammatory, anti-oxidant, and anti-proliferative effects, as well as favorable effects on endothelial function. Overall, the observational data suggest a benefit, but results are mixed and likely confounded by lifestyle and background dietary factors. The weight of evidence indicates favorable effects on risk factors and a number of plausible mechanisms have been elucidated in experimental and translational human studies. Despite the growing body evidence, it remains uncertain whether tea consumption should be recommended to the general population or to patients as a strategy to reduce cardiovascular risk.

Dietary flavonoid quercetin stimulates vasorelaxation in aortic vessels

Considerable epidemiological evidence indicates that dietary consumption of moderate levels of polyphenols decreases both the incidence of cardiovascular disease and the mortality associated with myocardial infarction. Molecular mechanisms of this cardiovascular protection remain uncertain but can involve changes in rates of nitric oxide (NO) generation by endothelial nitric oxide synthase (eNOS). We examined the vascular responses to quercetin using a combination of biochemical and vessel function criteria. Quercetin treatment for 30min enhanced relaxation of rat aortic ring segments. Moreover, the addition of L-NAME (100muM) or charybdotoxin (ChTx) blocked quercetin-mediated vasorelaxation thus demonstrating the effect was partially dependent on NOS and endothelium-derived hyperpolarizing factor (EDHF). Additionally, bovine aortic endothelial cells (BAEC) treated with quercetin showed a rapid increase of intracellular Ca(2+) concentrations as well as a dose- and time-dependent stimulation of eNOS phosphorylation with a concomitant increase in NO production. These results demonstrate that quercetin-mediated stimulation of eNOS phosphorylation increases NO bioavailability in endothelial cells and can thus play a role in the vascular protective effects associated with improved endothelial cell function.

Preventive effect of rutin, a bioflavonoid, on lipid peroxides and antioxidants in isoproterenol-induced myocardial infarction in rats

The consumption of diets rich in plant foods is associated with a reduced risk of cardiovascular diseases. This study aimed to evaluate the preventive role of rutin on lipid peroxides and antioxidants in normal and isoproterenol-induced myocardial infarction in rats. Subcutaneous injection of isoproterenol (150 mg kg−1) to male Wistar rats at an interval of 24 h for two days showed a significant increase in the activity of serum cardiac marker enzymes (creatine kinase, lactate dehydrogenase, aspartate transaminase and alanine transaminase) and a significant decrease in the activity of these enzymes in the heart. Lipid peroxidative products (thiobarbituricacid reactive substances and lipid hydroperoxides) were significantly increased and enzymic (superoxide dismutase, catalase and glutathione peroxidase) and non-enzymic (reduced glutathione and vitamin C) antioxidants showed a significant decrease in isoproterenol-treated rats. Pretreatment with rutin (40 or 80 mg kg−1) to isoproterenol-treated rats orally for a period of 42 days daily caused a significant effect. Administration of rutin to normal rats did not have any significant effect on any of the parameters studied. The results of our study show that rutin possesses antioxidant activity in isoproterenol-induced experimental myocardial infarction.

Green tea catechins and their oxidative protection in the rat eye

Catechins, active constituents of green tea, are well-known antioxidative natural products. It was proposed that green tea extract (GTE) consumption could benefit the eye, and the pharmacokinetics of catechins and oxidation status in rat eye were investigated after oral administration. Sprague-Dawley rats were fed GTE and sacrificed at different time intervals. Their eyes were dissected into cornea, lens, retina, choroid-sclera, vitreous humor, and aqueous humor for analysis of catechins and 8-epi-isoprostane by HPLC-ECD and GC-NCI-MS, respectively. Catechins were differentially distributed in eye tissues. Gallocatechin was present at the highest concentration in the retina, 22729.4 +/- 4229.4 pmol/g, and epigallocatechin in aqueous humor at 602.9 +/- 116.7 nM. The corresponding area-under-curves were 207,000 pmol x h/g and 2035.0 +/- 531.7 nM x h, respectively. The time of maximum concentration of the catechins varied from 0.5 to 12.2 h. Significant reductions in 8-epi-isoprostane levels were found in the compartments except the choroid-sclera or plasma, indicating antioxidative activities of catechins in these tissues.

Plant polyphenols in cancer and heart disease: implications as nutritional antioxidants

Certain dietary antioxidants such as vitamin E and vitamin C are important for maintaining optimum health. There is now much interest in polyphenolic products of the plant phenylpropanoid pathway as they have considerable antioxidant activity in vitro and are ubiquitous in our diet. Rich sources include tea, wine, fruits and vegetables although levels are affected by species, light, degree of ripeness, processing and storage. This confounds the formulation of databases for the estimation of dietary intakes. Most attention to date has focused on the flavonoids, a generic term which includes chalcones, flavones, flavanones, flavanols and anthocyanins. There is little convincing epidemiological evidence that intakes of polyphenols are inversely related to the incidence of cancer whereas a number of studies suggest that high intakes of flavonoids may be protective against CHD. In contrast, numerous cell culture and animal models indicate potent anticarcinogenic activity by certain polyphenols mediated through a range of mechanisms including antioxidant activity, enzyme modulation, gene expression, apoptosis, upregulation of gap junction communication and P-glycoprotein activation. Possible protective effects against heart disease may be due to the ability of some polyphenols to prevent the oxidation of LDL to an atherogenic form although anti-platelet aggregation activity and vasodilatory properties are also reported. However, some polyphenols are toxic in mammalian cells. Thus, until more is known about their bioavailability, metabolism and intracellular location, increasing intakes of polyphenols by supplements or food fortification may be unwise.

In vivo study of propolis supplementation effects on antioxidative status and red blood cells

In vivo study has been conducted on 47 healthy women and men in order to investigate whether daily intake of powdered propolis extract during 30 days has any influence on the following blood parameters: activity of superoxide dismutase, glutathione peroxidase and catalase, concentration of plasma malondialdehyde, total cholesterol, low- and high-density lipoprotein cholesterol, triglycerides, glucose, uric acid, ferritin and transferrin, together with routine red blood cell parameters. The effect of daily propolis intake seems to be time and gender related. For the men test group after the initial 15 days of propolis treatment, 23.2% (p=0.005) decrease in concentration of malondialdehyde was observed. After 30 days of treatment, statistically significant (p=0.010) 20.9% increase in superoxide dismutase activity and change in some of the red blood cell parameters were detected. For the women test group, the propolis treatment did not induce a change in any of the measured parameters.

Green tea extract only affects markers of oxidative status postprandially: lasting antioxidant effect of flavonoid-free diet

Epidemiological studies suggest that foods rich in flavonoids might reduce the risk of cardiovascular disease and cancer. The objective of the present study was to investigate the effect of green tea extract (GTE) used as a food antioxidant on markers of oxidative status after dietary depletion of flavonoids and catechins. The study was designed as a 2×3 weeks blinded human cross-over intervention study (eight smokers, eight non-smokers) with GTE corresponding to a daily intake of 18·6 mg catechins/d. The GTE was incorporated into meat patties and consumed with a strictly controlled diet otherwise low in flavonoids. GTE intervention increased plasma antioxidant capacity from 1·35 to 1·56 (P<0·02) in postprandially collected plasma, most prominently in smokers. The intervention did not significantly affect markers in fasting blood samples, including plasma or haemoglobin protein oxidation, plasma oxidation lagtime, or activities of the erythrocyte superoxide dismutase, glutathione peroxidase, glutathione reductase and catalase. Neither were fasting plasma triacylglycerol, cholesterol, α-tocopherol, retinol, β-carotene, or ascorbic acid affected by intervention. Urinary 8-oxo-deoxyguanosine excretion was also unaffected. Catechins from the extract were excreted into urine with a half-life of less than 2 h in accordance with the short-term effects on plasma antioxidant capacity. Since no long-term effects of GTE were observed, the study essentially served as a fruit and vegetables depletion study. The overall effect of the 10-week period without dietary fruits and vegetables was a decrease in oxidative damage to DNA, blood proteins, and plasma lipids, concomitantly with marked changes in antioxidative defence.

Uptake and distribution of catechins in fetal organs following in utero exposure in rats

BACKGROUND

Although catechins are known to be powerful antioxidants, no reports have shown their transport to fetal organs. We investigated the distribution of catechins in fetal rat organs after maternal exposure to green tea extract (GTE).

METHODS

GTE (550 mg/kg) or water was fed orally to pregnant dams at 15.5 days of gestation, the dams were sacrificed and fetal organs were dissected 0, 0.5, 1, 2, 3, 5, and 8 h later. Catechins and catechin gallates were determined by high-performance liquid chromatography (HPLC) after solid-phase extraction.

RESULTS

In the GTE-treated group, catechins were detected in most of the fetal organs studied, including the brain, eyes, heart, lungs, kidneys and liver but not in the control group. The first peak times (T(max)) were about 0.5-1 h. The maximum concentrations (C(max)) of catechins in the fetal eye were about 2-10 times higher than in the other organs, ranging from 249 pmol/g for epicatechin (EC) to 831 pmol/g for epigallocatechin gallate (EGCG). Catechin gallates were generally more readily taken up by fetal organs than catechins. EGCG had the highest level of uptake according to area under the curve (AUC) plots and the highest C(max) in all organs.

CONCLUSIONS

Various fetal organs had low but significant levels of catechins after GTE intake by the dams, and organ levels were found to be related to catechin structure. EGCG could be a potential candidate for antioxidant supplementation of the fetus in utero.

Effects of (-)-epigallocatechin-3-gallate on pancreatic beta-cell damage in streptozotocin-induced diabetic rats

Oxygen free radicals, which are produced as a result of chronic hyperglycemia, are implicated in many diabetic complications. (-)-Epigallocatechin-3-gallate (EGCG), a green tea polyphenol, has been shown to have both antioxidant and pro-oxidant activities, but its effect on oxidative stress of pancreatic beta cells in vivo is unclear. Here we evaluated the effects of nanomolar concentrations of EGCG on beta-cell survival and the response to high glucose loading in streptozotocin-induced diabetic rats. A 4-day intraperitoneal treatment with EGCG (5 mg/kg/day) further impaired the beta-cell response to high glucose in the diabetic rats. EGCG exacerbated the loss of islet cell mass and insulin-immunoreactivity in beta cells. These results suggest that, even at nanomolar plasma concentrations, EGCG acts as a pro-oxidant rather than an antioxidant, at least in beta cells in vivo.

Resveratrol, but not EGCG, in the diet suppresses DMBA-induced mammary cancer in rats

Despite the advent of new and aggressive therapeutics, breast cancer remains a leading killer among women; hence there is a need for the prevention of this disease. Several naturally occurring polyphenols have received much attention for their health benefits, including anti-carcinogenic properties. Two of these are resveratrol, a component of red grapes, and epigallocatechin-3-gallate (EGCG), the major catechin found in green tea. In this study, we tested the hypothesis that these two polyphenols protect against chemically-induced mammary cancer by modulating mammary gland architecture, cell proliferation, and apoptosis. Female Sprague-Dawley CD rats were exposed to either resveratrol (1 g/kg AIN-76A diet), EGCG (0.065% in the drinking water), or control diet (AIN-76A) for the entirety of their life starting at birth. At 50 days postpartum, rats were treated with 60 mg dimethylbenz[a]anthracene (DMBA)/kg body weight to induce mammary cancer. Resveratrol, but not EGCG, suppressed mammary carcinogenesis (fewer tumors per rat and longer tumor latency). Analysis of mammary whole mounts from 50-day-old rats revealed that resveratrol, but not EGCG, treatment resulted in more differentiated lobular structures. Bromodeoxyuridine (BrdU) incorporation studies showed that resveratrol treatment caused a significant reduction in proliferative cells in mammary terminal ductal structures at 50 days postpartum, making them less susceptible to carcinogen insult. The epithelial cells of terminal end buds in the mammary glands of resveratrol-treated rats also showed an increase in apoptotic cells compared to the control or EGCG-treated rats as measured by a DNA fragmentation assay. At the given doses, resveratrol treatment resulted in a serum resveratrol concentration of 2.00 μM, while treatment with EGCG resulted in a serum EGCG concentration of 31.06 nM. 17β-Estradiol, progesterone, and prolactin concentrations in the serum were not significantly affected by resveratrol or EGCG. Neither polyphenol treatment resulted in toxicity as tested by alterations in body weights, diet and drink consumptions, and day to vaginal opening. We conclude that resveratrol in the diet can reduce susceptibility to mammary cancer, while EGCG in the drinking water at the dose used was not effective.

Preventive action of green tea from changes in the liver antioxidant abilities of different aged rats intoxicated with ethanol

OBJECTIVE

The present study investigated the influence of green tea as a source of water-soluble antioxidants on the liver antioxidant potential of different aged rats chronically intoxicated with ethanol.

METHODS

Rats (2, 12, and 24 mo old) were fed for 5 wk on a control or an ethanol Lieber-DeCarli diet with and without green tea (7 g/L). The activity and level of enzymatic and non-enzymatic antioxidants and the level of markers of protein and lipid oxidation in the liver of rats were examined.

RESULTS

The activities of superoxide dismutase and catalase and levels of vitamins C, E, A, and beta-carotene were significantly decreased, whereas activities of glutathione peroxidase and glutathione reductase and the level of reduced glutathione significantly increased during aging. The ethanol diet caused a significant decrease in activity of antioxidant enzymes and in the level of non-enzymatic antioxidants tested. Administration of green tea to ethanol-treated rats of different ages partly normalized the activity of enzymes and the level of non-enzymatic antioxidants. Changes in antioxidant ability observed during aging were accompanied by increased levels of markers of lipid and protein modifications that also were intensified by ethanol. Green tea caused a decrease in lipid and protein oxidation in aged and ethanol-treated rats. The protective effect of green tea was confirmed by the significantly lower activity of biomarkers of liver damage (alanine and aspartate aminotransferases) in the serum of rats that received green tea with ethanol compared with rats from the control ethanol group.

CONCLUSIONS

The use of green tea appears to be beneficial to rat liver by decreasing oxidative stress caused by ethanol and/or aging.

Protective effect of green tea on erythrocyte membrane of different age rats intoxicated with ethanol

It is known that aging is characterized by changes in cell metabolism resulting in modification of the structure and function of cell membrane components which is mainly the consequence of reactive oxygen species action. These disturbances are also enhanced by different xenobiotics, e.g. ethanol. Therefore, the aim of this paper is to examine green tea influence on total antioxidant status (TAS) and on composition and electric charge of erythrocyte membrane phospholipids in ethanol intoxicated rats of various ages. Antioxidant abilities of erythrocytes were estimated by measuring TAS. Qualitative and quantitative composition of phospholipids in the membrane was determined by HPLC, while the extent of erythrocytes lipid peroxidation was estimated by HPLC measurement of malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE) levels. Electrophoresis was used to determine the surface charge density of the rat erythrocyte membrane. It was shown that the process of aging was accompanied by a decrease in TAS and in the total amount of phospholipids as well as by enhancement of lipid peroxidation and increase in surface charge density of erythrocyte membrane. Ethanol administration caused, in term, decrease in TAS and increase in the level of all phospholipids and lipid peroxidation products. Ethanol as well significantly enhanced changes in surface charge density of erythrocyte membrane. The ingestion of green tea partially prevented decrease in erythrocyte antioxidant abilities observed during aging and ethanol intoxication. Moreover, long-term drinking of green tea protects the structure of the erythrocytes membrane disturbed during aging process and/or chronic ethanol intoxication.

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.

Wine Ingestion Has No Effect on Lipid Peroxidation Products

OBJECTIVE

Moderate alcohol consumption has been associated with beneficial effects on coronary heart disease. This positive effect has been partly attributed to the flavonol contents which promote vasodilatory, anti-aggregatory and antioxidative effects and protect low-density lipoprotein (LDL) cholesterol from oxidation. Thus, the present study was carried out to determine the acute effects of different wines on LDL oxidization in healthy volunteers.

METHODS

Healthy male and female subjects (15/group) on a flavonol-restricted diet were randomly assigned to drink 300 ml wine from one of four different grapes and fermentation processes. Conjugated fatty acid dienes and thiobarbituric acid reactive substances (TBARS) were determined as a measure of LDL oxidation in serum at baseline and up to 96 h after wine ingestion.

RESULTS

At baseline, mean conjugated dienes in serum were 12.5+/-6.2 micromol/l and mean TBARS in serum were 15.7+/-8.1 micromol/l. There were no differences between the groups and no effect of any wine type on conjugated dienes (p=0.15) or TBARS (p=0.38) over time. 96 h following wine ingestion, the mean conjugated dienes were 12.1+/-4.12 micromol/l and mean TBARS were 16.4+/-8.8 micromol/l (pooled data, n=60).

CONCLUSION

Ingestion of 300 ml wine does not protect LDL from oxidation in vivo in healthy subjects. However, this does not exclude an effect of habitual wine consumption on LDL plasma oxidation.

Effect of flavonoids on stress responses in myotube cultures

Effects of flavonoids on stress response of myotube cultures was studied by monitoring the release of [14C] taurine, leukotriene production, and 2',7'-dichlorodihydroflourescein (DCFH2) oxidation. Stress was induced by hypotonic shock, which was accompanied by cell swelling leading to increased leukotriene production and a concomitant increase in reactive oxygen species and osmolyte release. In this model system, addition of the flavonoids catechin and quercetin decreased leukotriene production, DCFH2 oxidation, and taurine efflux, indicating a reduction of cellular stress. High concentrations of epigallocatechin gallate (EGCG) and tea extract increased leukotriene production and initial DCFH2 oxidation, indicating an increased cellular stress (possibly toxicity). However, taurine efflux was reduced, and also longer exposure time as well as lower concentrations of EGCG and tea reduced DCFH2 oxidation. Trolox and alpha-tocopherol did not significantly affect taurine efflux or leukotriene production, and it was therefore concluded that suppression of these responses was not confined to redox activity in a myotube culture.

Green tea protection against age-dependent ethanol-induced oxidative stress

Ethanol intoxication leads to oxidative stress, which may be additionally enhanced by aging. The aim of this study was to investigate the influence of green tea as a source of water-soluble antioxidants on the ability to prevent oxidative stress in aged rats sub-chronically intoxicated with ethanol. Two-, 12-, and 24-mo-old male Wistar rats were divided into 4 experimental groups: (1) control, (2) green tea, (3) ethanol, and (4) ethanol and green tea. Ethanol intoxication produced age-dependent decrease in the activity of serum superoxide dismutase, glutathione peroxidase, and reductase and in levels of glutathione (GSH), vitamins C, E, and A, and beta-carotene. Changes in the serum antioxidative ability were accompanied by enhanced oxidative modification of lipid (increase in lipid hydroperoxides, malondiadehyde, and 4-hydroxynonenal levels) and protein (rise in carbonyl group levels). Green tea partially protected against changes in antioxidant enzymatic as well as nonenzymatic parameters produced by ethanol and enhanced by aging. Administration of green tea significantly protects cellular components such as lipids and proteins against oxidative modification. Results indicate that green tea effectively protects blood serum against oxidative stress produced by ethanol as well as aging.

Mechanisms of cancer prevention by tea constituents

Consumption of tea (Camellia sinensis) has been suggested to prevent cancer, heart disease and other diseases. Animal studies have shown that tea and tea constituents inhibit carcinogenesis of the skin, lung, oral cavity, esophagus, stomach, liver, prostate and other organs. In some studies, the inhibition correlated with an increase in tumor cell apoptosis and a decrease in cell proliferation. Studies with human cancer cell lines have demonstrated that epigallocatechin-3-gallate (EGCG), a major tea polyphenol, inhibits mitogen-activated protein kinases, cyclin-dependent kinases, growth factor-related cell signaling, activation of activator protein 1 (AP-1) and nuclear factor kappaB (NFkappaB), topoisomerase I and matrix metalloproteinases as well as other potential targets. Although some studies report effects of EGCG at submicromolar levels, most experiments require concentrations of >10 or 20 micromol/L to demonstrate the effect. In humans, tea polyphenols undergo glucuronidation, sulfation, methylation, and ring fission. The peak plasma concentration of EGCG is approximately 1 micromol/L. The possible relevance of each of the proposed mechanisms to human cancer prevention is discussed in light of current bioavailability data for tea polyphenols and the potential limitations of animal models of carcinogenesis. Such discussion, it is hoped, will clarify some misunderstandings of cancer prevention by tea and stimulate new research efforts.

Antioxidant Effects of Tea: Evidence from Human Clinical Trials

Tea remains the most consumed drink in the world after water, well ahead of coffee, beer, wine and carbonated soft drinks. An accumulated number of population studies suggests that consumption of green and black tea beverages may bring positive health effects (1). One hypothesis explaining such effects is that the high levels of flavonoids in tea can protect cells and tissues from oxidative damage by scavenging oxygen-free radicals. Chemically, the flavonoids found in green and black tea are very effective radical scavengers. The tea flavonoids may therefore be active as antioxidants in the digestive tract or in other tissues after uptake. A substantial number of human intervention studies with green and black tea demonstrates a significant increase in plasma antioxidant capacity in humans approximately 1 h after consumption of moderate amounts of tea (1-6 cups/d). There are initial indications that the enhanced blood antioxidant potential leads to reduced oxidative damage to macromolecules such as DNA and lipids. However, the measurement of oxidative damage through biomarkers needs to be further established. In conclusion, tea flavonoids are potent antioxidants that are absorbed from the gut after consumption. Tea consumption consistently leads to a significant increase in the antioxidant capacity of the blood. Beneficial effects of increased antioxidant capacity in the body may be the reduction of oxidative damage to important biomolecules. The scientific support is strongest for the protection of DNA from oxidative damage after black or green tea consumption. However, the quality of the studies now available is insufficient to draw firm conclusions. Therefore, further evidence from human intervention studies is required.

Black tea extract supplementation decreases oxidative damage in Jurkat T cells

The purpose of this study was to investigate the protective effect of black tea (BT) extract against induced oxidative damage in Jurkat T-cell line. Cells supplemented with 10 or 25 mg/L BT were subjected to oxidation with ferrous ions. Malondialdehyde (MDA) production as marker of lipid peroxidation, DNA single strand breaks as marker of DNA damage, and modification of the antioxidant enzyme activity, glutathione peroxidase (GPX) were measured. Results show the efficacy of BT polyphenols to decrease DNA oxidative damage and to affect GPX activity (P<0.05), while no effect was shown on MDA production. The succeeding investigation of the activity of caffeine and epigallocatechin gallate demonstrated their antioxidant potential with respect to the cellular markers evaluated. In conclusion, this study supports the protective effect of BT against ferrous ions induced oxidative damage to DNA and the ability of BT to affect the enzyme antioxidant system of Jurkat cells.

NMR-based metabonomic studies on the biochemical effects of epicatechin in the rat

Flavonoid consumption via tea drinking has been attributed a number of potential health benefits including cancer prevention, anti-inflammatory action, and cardioprotectant activity. Although the predominant flavonoids in fresh leaf and green tea are known to be flavan-3-ols and flavan-3-O-gallates ("the catechins"), the biochemical effects of tea polyphenol consumption on living systems are generally poorly understood. Metabonomic methods utilizing (1)H NMR spectroscopy of biofluids and principal component analysis (PCA) have been applied to investigate the bioavailability and metabolic responses of rats to a single dose of 22 mg of epicatechin (EC) dissolved in water. Urine samples were collected twice daily (0-8 and 8-24 h) from male Sprague-Dawley rats (n = 10) prior to dosing and for 2 days after dosing. A series of subtle urinary biochemical effects were evident from the (1)H NMR spectra showing that EC was both bioavailable and biochemically active. The identifiable biochemical effects associated with EC dosing included decreased urinary concentrations of taurine, citrate, dimethylamine, and 2-oxoglutarate. These effects were predominately seen within the first 8 h after dosing. EC metabolites were also observed in the urine during this time period. PCA of later time points after dosing (24-32 and 32-48 h) showed that the effects of EC were reversible. This is the first in vivo study demonstrating the overall endogenous metabolic effects of EC consumption and shows the bioavailability of EC via metabolic effects and excretion of EC metabolites.

(-)-Epigallocatechin-3-gallate prevents oxidative damage in both the aqueous and lipid compartments of human plasma

When human plasma was exposed to the hydrophilic radical initiator, AAPH, (-)-epigallocatechin-(3)-gallate (EGCG) dose-dependently inhibited the aqueous compartment oxidation (IC(50)=0.72 microM) (monitored by DCFH oxidation) and spared the lipophilic antioxidants, alpha-tocopherol, and carotenoids, but not ascorbic acid. When radicals were selectively induced in the lipid compartment by the lipophilic radical initiator, MeO-AMVN, EGCG spared alpha-tocopherol, but not carotenoids and inhibited the lipid compartment oxidation (monitored by BODIPY 581/591) with a potency lower than that found in the aqueous compartment (IC(50)=4.37 microM). Our results indicate that EGCG, mainly localized in the aqueous compartment, effectively quenches aqueous radical species, thus limiting their diffusion into the lipid compartment and preventing lipid-soluble antioxidant depletion. Further, ESR experiments confirmed that EGCG recycled alpha-tocopherol through a H-transfer mechanism at the aqueous/lipid interface affording an additional protective mechanism to the lipid compartment of plasma.

Buckwheat honey increases serum antioxidant capacity in humans

Honey has been known to exert significant in vitro antioxidant activity, in part due to its phenolic content. However, conclusions that the antioxidants in honey are or are not efficacious in the human body cannot be reached if its antioxidant action is not assessed as part of a human study. In the present study, the acute effect of consumption of 500 mL of water, water with buckwheat honey, black tea, black tea with sugar, or black tea with buckwheat honey on serum oxidative reactions was examined in 25 healthy men. Antioxidant capacity of human serum samples was measured using different methods: the oxygen radical absorbance capacity (ORAC) assay, ex vivo susceptibility of serum lipoprotein to Cu(2+)-induced oxidation, and the thiobarbituric acid reactive substances (TBARS) assay. The results showed that the serum antioxidant capacity determined by ORAC increased significantly (p < 0.05) by 7% following consumption of buckwheat honey in water. No significant changes in serum antioxidant capacity could be established after the consumption of any of the other beverages. Ex vivo serum lipoprotein oxidation and TBARS values were not significantly altered after consumption of any of the five beverages. This study provides primary evidence of the in vivo antioxidant activity of buckwheat honey. However, long-term studies and epidemiological data are necessary to investigate whether honey consumption can exert overall antioxidant-related health benefits.

The biochemistry and medical significance of the flavonoids

Flavonoids are plant pigments that are synthesised from phenylalanine, generally display marvelous colors known from flower petals, mostly emit brilliant fluorescence when they are excited by UV light, and are ubiquitous to green plant cells. The flavonoids are used by botanists for taxonomical classification. They regulate plant growth by inhibition of the exocytosis of the auxin indolyl acetic acid, as well as by induction of gene expression, and they influence other biological cells in numerous ways. Flavonoids inhibit or kill many bacterial strains, inhibit important viral enzymes, such as reverse transcriptase and protease, and destroy some pathogenic protozoans. Yet, their toxicity to animal cells is low. Flavonoids are major functional components of many herbal and insect preparations for medical use, e.g., propolis (bee's glue) and honey, which have been used since ancient times. The daily intake of flavonoids with normal food, especially fruit and vegetables, is 1-2 g. Modern authorised physicians are increasing their use of pure flavonoids to treat many important common diseases, due to their proven ability to inhibit specific enzymes, to simulate some hormones and neurotransmitters, and to scavenge free radicals.

The mechanism of action of antioxidants against lipoprotein peroxidation, evaluation based on kinetic experiments

Peroxidation of blood lipoproteins is regarded as a key event in the development of atherosclerosis. Hence, attenuation of the oxidative modification of lipoproteins by natural and synthetic antioxidants in vivo is considered a possible way of prevention of cardiovascular disorders. The assessment of the susceptibility of lipoproteins to oxidation is commonly based on in vitro oxidation experiments. Monitoring of oxidation provides the kinetic profile characteristic for the given lipoprotein preparation. The kinetic profile of peroxidation is characterized by three major parameters: the lag preceding rapid oxidation, the maximal rate of oxidation (V(max)) and the maximal accumulation of oxidation products (OD(max)). Addition of antioxidants alters this pattern, affecting the kinetic parameters of oxidation. In particular, antioxidants may prolong the lag and/or decrease the V(max) and/or decrease the OD(max). Such specific variation of the set of kinetic parameters may provide important information on the mechanism of the inhibitory action of a given antioxidant (scavenging free radicals, metal-binding or other mechanisms). Numerous natural and synthetic compounds were reported to inhibit oxidation of lipoproteins. Based on the analysis of reported effects and theoretical considerations, we propose a simple protocol that relates the kinetic effects of a given antioxidant to the mechanism of its action.

Green tea as a potent antioxidant in alcohol intoxication

Ethanol oxidation to acetaldehyde and next to acetate is accompanied by free radical generation. Free radicals can affect cell integrity when antioxidant mechanisms are no longer able to cope with the free radical generation observed in ethanol intoxication. Natural antioxidants are particularly useful in such a situation. The present study was designed to investigate the efficacy of green tea as a source of water-soluble antioxidants (catechins) on the liver and blood serum antioxidative potential of rats chronically (28 days) intoxicated with ethanol. Alcohol caused a decrease in liver superoxide dismutase, glutathione peroxidase and catalase activities and an increase in activity of glutathione reductase. Moreover, a decrease in the level of reduced glutathione, ascorbic acid, vitamins A and E and beta-carotene were observed. The activity of serum glutathione peroxidase decreased while glutathione reductase activity increased. The level of serum non-enzymatic antioxidants was also decreased in the liver. Alcohol administration caused an increase in the liver and serum lipid peroxidation products, measured as thiobarbituric acid-reactive substances. However, green tea prevents the changes observed after ethanol intoxication. Green tea also protects membrane phospholipids from enhanced peroxidation. These results indicate a beneficial effect of green tea in alcohol intoxication.

The role of tea in human health: an update

Tea is an important dietary source of flavanols and flavonols. In vitro and animal studies provide strong evidence that tea polyphenols may possess the bioactivity to affect the pathogenesis of several chronic diseases, especially cardiovascular disease and cancer. However, the results from epidemiological and clinical studies of the relationship between tea and health are mixed. International correlations do not support this relationship although several, better controlled case-referent and cohort studies suggest an association with a moderate reduction in the risk of chronic disease. Conflicting results between human studies may arise, in part, from confounding by socioeconomic and lifestyle factors as well as by inadequate methodology to define tea preparation and intake. Clinical trials employing putative intermediary indicators of disease, particularly biomarkers of oxidative stress status, suggest tea polyphenols could play a role in the pathogenesis of cancer and heart disease.

Evaluation of antioxidant activity of epigallocatechin gallate in biphasic model systems in vitro

The antioxidant activity of epigallocatechin gallate (EGCG) was studied in different in vitro model systems, which enabled evaluation of both chemical and physical factors involved in assessing the role of EGCG in oxidative reactions. EGCG suppressed the initiation rate and prolonged the lag phase duration of peroxyl radical-induced oxidation in a phospholipid liposome model to a greater extent (p < 0.01) compared to both Trolox and alpha-tocopherol. Effectiveness of these antioxidants to prolong the peroxyl radical-induced lag phase was inversely related to lipophilic character. EGCG also protected against both peroxyl radical and hydroxyl radical-induced supercoiled DNA nicking. The rate constant describing EGCG reaction against hydroxyl radical was 4.22+/-0.07 x 10(10) M(-1) x sec(-1), which was comparable to those of Trolox and alpha-tocopherol, respectively. EGCG exhibited a synergistic effect with alpha-tocopherol in scavenging 1,1-diphenyl-2-picylhydrazyl (DPPH) radical, thus displaying a direct free radical scavenging capacity. In vitro Cu2+-induced-human LDL oxidation was accelerated in the presence of EGCG and attributed to the conversion of Cu2+ to Cu+. We conclude that the particularly effective antioxidant properties of EGCG noted in both chemical and biological biphasic systems were related to a unique hydrophilic and lipophilic balance which enabled effective free radical scavenging. The same chemical-physical properties of EGCG also enabled prooxidant activity, only when in contact with unbound transition metal ions in a multiphasic system.

The gastrointestinal tract: a major site of antioxidant action?

Diets rich in fruits and vegetables delay the onset of many age-related diseases, and contain a complex mixture of antioxidants (including ascorbate, carotenoids, vitamin E and other phenolics such as the flavonoids). However, diet also contains pro-oxidants, including iron, copper, H2O2, haem, lipid peroxides and aldehydes. Nitrite is frequently present in diet, leading to generation of reactive nitrogen species in the stomach. In considering the biological importance of dietary antioxidants, attention has usually focussed on those that are absorbed through the gastrointestinal tract into the rest of the body. In the present paper we develop the argument that the high levels of antioxidants present in certain foods (fruits, vegetables, grains) and beverages (e.g. green tea) play an important role in protecting the gastrointestinal tract itself from oxidative damage, and in delaying the development of stomach, colon and rectal cancer. Indeed, carotenoids and flavonoids do not seem to be as well absorbed as vitamins C and E. Hence their concentrations can be much higher in the lumen of the GI tract than are ever achieved in plasma or other body tissues, making an antioxidant action in the GI tract more likely. Additional protective mechanisms of these dietary constituents (e.g. effects on intercellular communication, apoptosis, cyclooxygenases and telomerase) may also be important.