Effect of dietary quercetin on oxidative DNA damage in healthy human subjects

In silico study of potential immunonutrient-based sports supplements against COVID-19 via targeting ACE2 inhibition using molecular docking and molecular dynamics simulations

Use of some sports supplements can inhibit angiotensin-converting enzyme II (ACE2), a receptor for the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), as reviewed through molecular docking and sequent molecular dynamics (MD) simulations against this condition. The crystal structures of ACE2 receptors of SARS-CoV-2 and SARS-CoV, applied in docking analysis, were taken from the Protein Data Bank (PDB). The receptors were then prepared using the Molecular Operating Environment (MOE), as a drug-discovery software platform for docking. Supplements such as quercetin and beta glucan (β-glucan) were the top docked compounds to ACE2 receptor though they strongly interacted with CoV target protein. The study data showed that immune responses to immunonutrient-based sports compounds (viz. quercetin and β-glucan) in Coronavirus disease 2019 (COVID-19) were essential in mounting successful immune responses by athletes. While awaiting the development of an effective vaccine, there is a need to focus on immunonutrient-based sports supplements as preventive and therapeutic options that can be implemented in a safe and quick manner to bolster immune responses in athletes.Communicated by Ramaswamy H. Sarma.

A Review of Twenty Years of Research on the Regulation of Signaling Pathways by Natural Products in Breast Cancer

Breast cancer (BC) is the second leading cause of death among women, and it has become a global health issue due to the increasing number of cases. Different treatment options, including radiotherapy, surgery, chemotherapy and anti-estrogen therapy, aromatase inhibitors, anti-angiogenesis drugs, and anthracyclines, are available for BC treatment. However, due to its high occurrence and disease progression, effective therapeutic options for metastatic BC are still lacking. Considering this scenario, there is an urgent need for an effective therapeutic strategy to meet the current challenges of BC. Natural products have been screened as anticancer agents as they are cost-effective, possess low toxicity and fewer side effects, and are considered alternative therapeutic options for BC therapy. Natural products showed anticancer activities against BC through the inhibition of angiogenesis, cell migrations, proliferations, and tumor growth; cell cycle arrest by inducing apoptosis and cell death, the downstream regulation of signaling pathways (such as Notch, NF-κB, PI3K/Akt/mTOR, MAPK/ERK, and NFAT-MDM2), and the regulation of EMT processes. Natural products also acted synergistically to overcome the drug resistance issue, thus improving their efficacy as an emerging therapeutic option for BC therapy. This review focused on the emerging roles of novel natural products and derived bioactive compounds as therapeutic agents against BC. The present review also discussed the mechanism of action through signaling pathways and the synergistic approach of natural compounds to improve their efficacy. We discussed the recent in vivo and in vitro studies for exploring the overexpression of oncogenes in the case of BC and the current status of newly discovered natural products in clinical investigations.

Polyphenols and Human Health: The Role of Bioavailability

Polyphenols are a group of phytochemicals with potential health-promoting effects. They are classified as flavonoid (flavonols, flavanols, flavones, flavanones, isoflavones, and anthocyanins) and non-flavonoid molecules (phenolic acids, hydroxycinnamic acids, lignans, stilbenes, and tannins). Although an increasing number of trials have shown a correlation among polyphenol consumption and a reduction in risk factors for chronic diseases, discrepancies in explaining their positive effects have been found in terms of the bioavailability. In fact, polyphenols show a low bioavailability due to several factors: interaction with the food matrix, the metabolic processes mediated by the liver (phase I and II metabolism), intestine and microbiota. On the other hand, the biological activities of phenol compounds may be mediated by their metabolites, which are produced in vivo, and recent studies have confirmed that these molecules may have antioxidant and anti-phlogistic properties. This review discusses the studies performed in vivo, which consider the polyphenol bioavailability and their different food sources. Factors influencing the biological effects of the main classes of polyphenols are also considered.

Consumption of Fresh Yellow Onion Ameliorates Hyperglycemia and Insulin Resistance in Breast Cancer Patients During Doxorubicin-Based Chemotherapy: A Randomized Controlled Clinical Trial

PURPOSE

Doxorubicin has been found to be associated with insulin resistance in animal models. Onion, a so-called functional food, is noted to affect the insulin signaling pathway of diabetes in vitro. To our knowledge, this is the first study to investigate the effects of consuming fresh yellow onions on insulin-related indices compared with a low-onion-containing diet among breast cancer (BC) patients treated with doxorubicin.

METHODS

This parallel-design, randomized, triple-blind, controlled clinical trial was conducted on 56 eligible BC patients (aged 30-63 years), diagnosed with invasive ductal carcinoma. Following their second cycle of chemotherapy, subjects were assigned in a stratified-random allocation to receive body mass index-dependent 100 to 160 g/d of onion as high onion group (HO; n = 28) or 30 to 40 g/d small onions in low onion group (LO; n = 28) for 8 weeks intervention. Participants, care givers, and those who assessed laboratory analyses were blinded to the assignments (IRCT Registry No.: IRCT2012103111335N1).

RESULTS

The compliance level of participants in the analysis was as high as 87.85%. A total of 23 available cases was analyzed in each group. The daily use of HO resulted in a significant decrease in serum fasting blood glucose and insulin levels in comparison with LO, over the period of study ( P < .001). Posttreatment with HO showed a significant decrease in homeostasis model of assessment-insulin resistance relative to changes in the LO group ( P < .05). A comparison of the changes that occurred throughout pre- and postdose treatments indicated improved quantitative insulin sensitivity check index ( P < .05) and controls on C-peptide in the HO group ( P < .05).

CONCLUSIONS

The present study demonstrated the effectiveness of onion to ameliorate hyperglycemia and insulin resistance in BC during doxorubicin-based chemotherapy.

Effect of vitamin E supplementation on mRNA expression of superoxide dismutase and interleukin-2 in arsenic exposed goat leukocytes

The aim of this study was to quantify the expression level of genes involved in antioxidant defenses during inorganic arsenic (iAs) exposure in the blood of goats and to evaluate the regulative activity on these genes of antioxidant vitamin E in the diet. Twenty-four crossbred lactating goats (Alpine × Beetal) were distributed randomly into four equal groups (Control, T(1), T(2) and T(3)) of six in each, on the basis of average body weight (36.10 ± 0.11 kg) and milk yield (1.61 ± 0.004 kg/day). The animals in T(1), T(2) and T(3) were given 50 mg/kg dry matter arsenic daily, while in T(2) and T(3), vitamin E @100 IU and 150 IU/kg dry matter, respectively, was also supplemented additionally for the period of 12 months. Blood was sampled at 0 day then at 3 months interval and analyzed for the expression level of superoxide dismutase (Cu/Zn SOD) and interleukin-2 (IL-2) using real-time PCR technique. Initially there was no difference (p > 0.05) in relative expression of the two genes. But, at 3 months, relative expression of Cu/Zn SOD increased (p < 0.05) in T(1) groups then, at 6 and 9 months expression was decreased (p < 0.05) in all the iAs treated groups whereas at 12 months, vitamin E supplementation increased (p < 0.05) the expression which is comparable to control groups. IL-2 mRNA expression was decreased (p < 0.05) at 6 months in all iAs treated groups, at 9 months there was decline trend but not significantly different whereas at 12 months decline trend was less (p < 0.05) in vitamin E supplemented groups. The result suggests that vitamin E may have a controlling effect on oxidative stress through modulation of SOD and IL-2 expression.

Cherries and health: a review

Cherries, and in particular sweet cherries, are a nutritionally dense food rich in anthocyanins, quercetin, hydroxycinnamates, potassium, fiber, vitamin C, carotenoids, and melatonin. UV concentration, degree of ripeness, postharvest storage conditions, and processing, each can significantly alter the amounts of nutrients and bioactive components. These constituent nutrients and bioactive food components support the potential preventive health benefits of cherry intake in relation to cancer, cardiovascular disease, diabetes, inflammatory diseases, and Alzheimer's disease. Mechanistically, cherries exhibit relatively high antioxidant activity, low glycemic response, COX 1 and 2 enzyme inhibition, and other anti-carcinogenic effects in vitro and in animal experiments. Well-designed cherry feeding studies are needed to further substantiate any health benefits in humans.

Effects of Thai black sticky rice extract on oxidative stress and lipid metabolism gene expression in HepG2 cells

Anthocyanins, which are found in some food, including Thai black sticky rice, are reported to have health-promoting properties. Oxidative stress plays a major role in the pathogenesis of many degenerative diseases induced by free radicals, such as cardiovascular disease, stroke and cancer. We evaluated the anthocyanin-rich extract (ARE) from Thai black sticky rice for antioxidative and antihyperlipidemic effects on HepG2 cells. Cell viability was investigated with the neutral red assay and the MTT assay, and oxidative stress was determined by the DCFH-DA assay. RT-PCR was used to evaluate the effect of ARE on LDLR, HMG-CoAR, PPAR (α1,γ) and LXRa gene expression. We found that ARE at high doses (≥ 800 mg/L) induces cytotoxicity. However, at 600-1000 mg/L it reduced intracellular oxidative stress (P < 0.05) in a dose-dependent manner, and at 200 mg/L it significantly enhanced the expression of the LDLR gene in HepG2 cells. We concluded that ARE can be beneficial for health promotion by reducing oxidative stress and enhancing LDL clearance, regulating LDLR production on the cell surface membrane, thereby maintaining lipid homeostasis.

Role of dietary antioxidants in the prevention of in vivo oxidative DNA damage

Epidemiological evidence consistently shows that diets high in fresh fruit and vegetables significantly lower cancer risk. Given the postulated role of oxidative DNA damage in carcinogenesis, the assumption has been made that it is the antioxidant properties of food constituents, such as vitamin C, E and carotenoids, which confer protection. However, epidemiological studies with specific antioxidants, either singly or in combination, have not, on the whole, supported this hypothesis. In contrast, studies examining the in vitro effect of antioxidants upon oxidative DNA damage have generally been supportive, in terms of preventing damage induction. The same, however, cannot be said for the in vivo intervention studies where overall the results have been equivocal. Nevertheless, recent work has suggested that some dietary antioxidants may confer protective properties through a novel mechanism, unrelated to their conventional free-radical scavenging abilities. Upregulation of antioxidant defence, xenobiotic metabolism, or DNA-repair genes may all limit cellular damage and hence promote maintenance of cell integrity. However, until further work has clarified whether dietary supplementation with antioxidants confers a reduced risk of cancer and the mechanism by which this effect is exerted, the recommendation for a diet rich in fruit and vegetables remains valid empirically.

Chronic quercetin ingestion and exercise-induced oxidative damage and inflammation

Quercetin is a flavonoid compound that has been demonstrated to be a potent antioxidant in vitro. The objective of this study was to evaluate if quercetin ingestion would increase plasma antioxidant measures and attenuate increases in exercise-induced oxidative damage. Forty athletes were recruited and randomized to quercetin or placebo. Subjects consumed 1000 mg quercetin or placebo each day for 6 weeks before and during 3 d of cycling at 57% work maximum for 3 h. Blood was collected before and immediately after exercise each day, and analyzed for F2-isoprostanes, nitrite, ferric-reducing ability of plasma, trolox equivalent antioxidant capacity, and C-reactive protein. Statistical analyses involved a 2 (treatment) × 6 (times) repeated measures analysis of variance to test main effects. F2-isoprostanes, nitrite, ferric-reducing ability of plasma, trolox equivalent antioxidant capacity, and C-reactive protein were significantly elevated as a result of exercise, but no group effects were found. Despite previous data demonstrating potent antioxidant actions of quercetin in vitro, this study indicates that this effect is absent in vivo and that chronic quercetin ingestion does not exert protection from exercise-induced oxidative stress and inflammation.

Impact of multiple genetic polymorphisms on effects of a 4-week blueberry juice intervention on ex vivo induced lymphocytic DNA damage in human volunteers

Consumption of fruits and vegetables has been associated with a decrease in cancer incidence and cardiovascular disease, presumably caused by antioxidants. We designed a human intervention study to assess antioxidative and possible anti-genotoxic properties of fruit-borne antioxidants. We hypothesized that individuals bearing genetic polymorphisms for genes related to quercetin metabolism, benzo[a]pyrene metabolism, oxidative stress and DNA repair differ in their response to DNA protective effects of increased antioxidant intake. In the present study, 168 healthy volunteers consumed a blueberry/apple juice that provided 97 mg quercetin and 16 mg ascorbic acid a day. After a 4-week intervention period, plasma concentrations of quercetin and ascorbic acid and trolox equivalent antioxidant capacity (TEAC) were significantly increased. Further, we found 20% protection (P < 0.01) against ex vivo H(2)O(2)-provoked oxidative DNA damage, measured by comet assay. However, the level of ex vivo induced benzo[a]pyrene-diol-epoxide (BPDE)-DNA adducts was 28% increased upon intervention (P < 0.01). Statistical analysis of 34 biologically relevant genetic polymorphisms revealed that six significantly influenced the outcome of the intervention. Lymphocytes from individuals bearing variant genotype for Cyp1B1 5 seemed to benefit more than wild-types from DNA damage-protecting effects upon intervention. Variants for COMT tended to benefit less or even experienced detrimental effects from intervention. With respect to GSTT1, the effect is ambiguous; variants respond better in terms of intervention-related increase in TEAC, but wild-types benefit more from its protecting effects against oxidative DNA damage. We conclude that genotyping for relevant polymorphisms enables selecting subgroups among the general population that benefit more of DNA damage-modulating effects of micronutrients.

Quercetin exhibits a specific fluorescence in cellular milieu: a valuable tool for the study of its intracellular distribution

The elaboration of novel techniques for flavonoid intracellular tracing would elucidate the compounds' absorption and bioavailability and assist molecular and pharmacological approaches, as they are promising candidates for drug development. This study exploited the properties of quercetin (3,3',4',5,7-pentahydroxyflavone), found in high concentrations in the majority of edible plants. Through the use of UV-vis spectroscopy, confocal microscopy, and HPLC-ESI-MS, native quercetin, at physiologically relevant concentrations, was found to exhibit a specific fluorescence (488 nmex/500-540 nmem) upon internalization. This fluorescence shift is due to a non-covalent binding to intracellular targets (probably proteins) and compatible with the settings applied in confocal microscopy. This property provides a valuable, selective alternative technique for quercetin tracing in cellular systems, permitting the quantitative evaluation of its transit at pharmacologically relevant concentrations and the validation of a number of already described molecular functions.

Markers of oxidative DNA damage in human interventions with fruit and berries

Diets rich in fruit and vegetables are associated with a decreased risk of several cancers via numerous possible mechanisms. For example, phytochemicals may decrease oxidative DNA damage and enhance DNA repair. Markers of oxidative DNA damage in human dietary intervention trials used most frequently include oxidized nucleosides such as 7-hydro-8-oxo-2'-deoxyguanosine, which can be analyzed from isolated DNA or urine. Single-cell gel electrophoresis has been widely used to measure baseline or H2O2-induced DNA strand breaks or sites of modified bases sensitive to repair enzymes recognizing oxidized purines or pyrimidines. Recently, markers of DNA repair also have been used. Few controlled human dietary interventions have investigated the specific effects of fruit or berries. There are indications that kiwifruit can decrease H2O2 sensitivity of lymphocyte DNA ex vivo and enhance DNA repair. Carefully controlled studies with flavonoid-rich fruit or berry juices found only few significant differences; less rigorously controlled studies gave more optimistic results. Data on the effects of fruit and berries on DNA damage in humans are scarce and inconclusive; adequately controlled studies with validated markers are needed. Because levels of DNA damage are usually low in young healthy volunteers, groups with an enhanced risk of DNA damage should be studied.

Effect of Natural Antioxidants on Superoxide Dismutase and Glutathione Peroxidase mRNA Expression in Leukocytes from Periparturient Dairy Cows

During the peripartum period, high-yielding dairy cows experience metabolic stress, which alters their homeostasis and exposes the cows to illness. The aim of this study was to quantify the expression levels of genes involved in antioxidant defences during the transition period in the blood of dairy cows and to evaluate the regulative activity on these genes of natural antioxidants in the diet. Three groups of 7 heifers each, at the 7th month of pregnancy, were used. Starting from 3 weeks before the expected calving date (-22 days), the three groups were allotted to the following experimental treatments: control (CTR, basal diet); lycopene (LYC, basal diet + lycopene 540 mg/day) and grape polyphenols (POL, basal diet + grape polyphenols 10 g/day). Blood was sampled at 22 and 8 days before and 8, 15 and 22 after calving and analysed for the expression level of glutathione peroxidase (GPx) and superoxide dismutase (Cu/ZnSOD) using the real-time PCR technique with LUX (Light Upon eXtension) fluorogenic primers. During the peripartum period (-22 days until + 22 days from calving), Cu/ ZnSOD mRNA expression decreased (p<0.05) in the CTR and LYC groups, but increased at 15 days after calving in the POL group. No significant differences were found in GPx mRNA expression. The results suggest that grape polyphenols may have a controlling effect on peripartum metabolic stress through modulation of superoxide dismutase expression.

Dietary polyphenolic phytochemicals—promising cancer chemopreventive agents in humans? A review of their clinical properties

Epidemiological and preclinical evidence suggests that polyphenolic phytochemicals exemplified by epigallocatechin gallate from tea, curcumin from curry and soya isoflavones possess cancer chemopreventive properties. Whilst such naturally occurring polyphenols have been the subject of numerous mechanistic studies in cells, information on their clinical properties, which might help assess their promise as human cancer chemopreventive agents, is scarce. Therefore, we present a review of pilot studies and trials with a cancer chemoprevention-related rationale, in which either healthy individuals or patients with premalignant conditions or cancer received polyphenolic phytochemicals. The review identifies trial design elements specifically applicable to polyphenolic phytochemicals. The available evidence for tea polyphenols tentatively supports their advancement into phase III clinical intervention trials aimed at the prevention of progression of prostate intraepithelial neoplasia, leukoplakia or premalignant cervical disease. In the case of curcumin and soya isoflavones more studies in premalignacies seem appropriate to optimise the nature and design of suitable phase III trials. The abundance of flavonoids and related polyphenols in the plant kingdom makes it possible that several hitherto uncharacterised agents with chemopreventive efficacy are still to be identified, which may constitute attractive alternatives to currently used chemopreventive drugs.

Dietary polyphenols and the prevention of diseases

Polyphenols are the most abundant antioxidants in the diet and are widespread constituents of fruits, vegetables, cereals, dry legumes, chocolate, and beverages, such as tea, coffee, or wine. Experimental studies on animals or cultured human cell lines support a role of polyphenols in the prevention of cardiovascular diseases, cancers, neurodegenerative diseases, diabetes, or osteoporosis. However, it is very difficult to predict from these results the effects of polyphenol intake on disease prevention in humans. One of the reasons is that these studies have often been conducted at doses or concentrations far beyond those documented in humans. The few clinical studies on biomarkers of oxidative stress, cardiovascular disease risk factors, and tumor or bone resorption biomarkers have often led to contradictory results. Epidemiological studies have repeatedly shown an inverse association between the risk of myocardial infarction and the consumption of tea and wine or the intake level of some particular flavonoids, but no clear associations have been found between cancer risk and polyphenol consumption. More human studies are needed to provide clear evidence of their health protective effects and to better evaluate the risks possibly resulting from too high a polyphenol consumption.

Protection by quercetin and quercetin-rich fruit juice against induction of oxidative DNA damage and formation of BPDE-DNA adducts in human lymphocytes

Flavonoids are claimed to protect against cardiovascular disease, certain forms of cancer and ageing, possibly by preventing initial DNA damage. Therefore, we investigated the protective effects of the flavonoid quercetin against the formation of oxidative DNA damage and bulky DNA adducts in human lymphocytes, both in vitro and ex vivo. First, human lymphocytes were pre-incubated with various concentrations of quercetin, followed by incubation with hydrogen peroxide; protection against oxidative DNA damage was evaluated by use of the single-cell gel electrophoresis (Comet) assay. Second, quercetin-treated human lymphocytes were challenged by treatment with benzo(a)pyrene (B(a)P), and BPDE-DNA adduct formation was measured by (32)P-postlabelling. Third, in a pilot study, lymphocytes from female volunteers who consumed a quercetin-rich blueberry/apple juice mixture for four weeks, were treated ex vivo with an effective dose of H(2)O(2) and benzo(a)pyrene, respectively, at three different time points, i.e. before (t=0 weeks), during (t=2 weeks) and after (t=4 weeks) the intervention. Results in vitro: a significant dose-dependent protection by quercetin against both the formation of oxidative DNA damage (p<0.01) and of BPDE-DNA adducts (p<0.05) was observed. Results in vivo: four weeks of juice intervention led to a significant increase in the total antioxidant capacity of plasma, as reflected by the increase of the TEAC value from 773 microM trolox equivalent at t=0 to 855 microM at t=4 weeks (p=0.04) and an increase in plasma quercetin content from 5.0 to 10.6 nM (p=0.03). After intervention, the level of oxidative damage upon ex vivo exposure to H(2)O(2) was non-significantly (p=0.07) decreased by 41%, and the BPDE-DNA adduct level induced ex vivo was non-significantly decreased by 11%. The combination of our findings in vitro and ex vivo provides evidence that quercetin is able to protect against chemically induced DNA damage in human lymphocytes, which may underlie its suggested anticarcinogenic properties.

Potential biomedical properties of Pinus massoniana bark extract

This study examined the potential biomedical properties of a bark extract from Pinus massoniana Lamb (PMBE). Its antioxidant activity, superoxide anion radical scavenging and free radical scavenging activities were examined. The antioxidant activity in a linoleic acid emulsion increased with increasing amounts of PMBE, with 100, 300 and 500 microg PMBE inhibiting 64.7%, 68.6% and 76.6% of peroxidation, respectively. Similarly, the radical scavenging activity by PMBE increased in a dose-dependent manner, suggesting that there may be a correlation between the antioxidant and scavenging activities. In addition, the effect of PMBE on human hepatocellular carcinoma BEL-7402 cells and normal liver L-02 cells was investigated in vitro. PMBE appeared to inhibit selectively the growth of BEL-7402 and slightly promoted the growth of L-02. Taken together, the results indicate that PMBE is a natural antioxidant that could potentially be used as a food supplement or as a candidate precursor substance for new anticancer therapeutics.

Interventions with antioxidants and nutrients in relation to oxidative DNA damage and repair

Cells are constantly exposed to oxidants from metabolic and other biochemical reactions as well as external factors, suggesting that DNA repair systems and nutritional antioxidants are important determinants for low levels of DNA damage and cancer risk. The effects of single antioxidants, as well as various vegetables, fruits and carotenoid- and polyphenolic-rich products, have been assessed with biomarkers, mainly including DNA damage in white blood cells (WBC), urinary excretion of oxidized bases and nucleosides and DNA repair capacity. The basal levels of oxidative DNA damage, and effects of the interventions have been rather variable, possibly reflecting differences in the populations, regimens, and the type of assays. In general, single dose antioxidant interventions have shown protective effects with respect to WBC DNA oxidation. Studies with continuous ingestion of antioxidants show mixed results with respect to effects on oxidative DNA damage in WBC, possibly due to various problems with design, statistical power and period effects. Studies with only male subjects appear to show consistent antioxidant effects in terms of reduced levels of oxidized pyrimidines. Investigations of oxidatively stressed subjects, e.g. HIV-infected patients or diabetics, suggest beneficial outcomes in populations with high initial levels of oxidative DNA damage. Recent research on the effect of antioxidants on DNA repair enzymes suggest effects in terms of increased removal of oxidized purines, whereas mRNA levels of the relevant DNA repair genes appears to be unaffected by an antioxidant-rich diet. In the future, care should be taken with respect to design of intervention studies and considerations of gender effect, genotypes of defence enzymes as well as DNA repair capacity.

Phyto-oestrogens, their mechanism of action: current evidence for a role in breast and prostate cancer

The incidence of hormone-dependent cancers, such as those of the breast and prostate, is much lower in Eastern countries such as China and Japan in comparison with the Western world. Diet is believed to have a major effect on disease risk and one group of compounds, the phyto-oestrogens, which are consumed in large amounts in Asian populations, have been implicated in cancer protection. This view follows the finding that plasma and urinary levels of phyto-oestrogens are much higher in areas where cancer incidence is low in comparison with areas of high cancer incidence. The phyto-oestrogens are comprised of two main groups; the isoflavones and lignans. Of the isoflavones, genistein and daidzein have been the most widely studied. These compounds have been shown to possess anticancer properties; however their precise mechanism of action remains to be elucidated. In comparison, few studies have investigated the effects of lignans in breast and prostate cancer. In vitro studies have shown that genistein exerts biphasic effects on cancer cell growth, stimulating growth at low concentrations (<10 microm) and inhibiting growth at high concentrations (>10 microm), which suggests that low phyto-oestrogen levels may stimulate cancer growth in vivo. Plasma phyto-oestrogen concentrations of >10 microm cannot be achieved by dietary intake and therefore the timing of exposure to phyto-oestrogens may be of the utmost importance in determining their chemopreventive effects. The present paper reviews the effects of phyto-oestrogens on breast and prostate cancer in vivo and in vitro and discusses possible mechanisms of action via which these compounds may exert their effects.

Clinical pharmacokinetics of antioxidants and their impact on systemic oxidative stress

Dietary antioxidants play a major role in maintaining the homeostasis of the oxidative balance. They are believed to protect humans from disease and aging. Vitamin C (ascorbic acid), vitamin E (tocopherol), beta-carotene and other micronutrients such as carotenoids, polyphenols and selenium have been evaluated as antioxidant constituents in the human diet. This article addresses data provided from clinical trials, highlighting the clinical pharmacokinetics of vitamin C, vitamin E, beta-carotene, lycopene, lutein, quercetin, rutin, catechins and selenium. The bioavailability of vitamin C is dose-dependent. Saturation of transport occurs with dosages of 200-400 mg/day. Vitamin C is not protein-bound and is eliminated with an elimination half-life (t((1/2))) of 10 hours. In Western populations plasma vitamin C concentrations range from 54-91 micro mol/L. Serum alpha- and gamma-tocopherol range from 21 micro mol/L (North America) to 27 micro mol/L (Europe) and from 3.1 micro mol/L to 1.5 micro mol/L, respectively. alpha-Tocopherol is the most abundant tocopherol in human tissue. The bioavailability of all-rac-alpha-tocopherol is estimated to be 50% of R,R,R-alpha-tocopherol. The hepatic alpha-tocopherol transfer protein (alpha-TTP) together with the tocopherol-associated proteins (TAP) are responsbile for the endogenous accumulation of natural alpha-tocopherol. Elimination of alpha-tocopherol takes several days with a t((1/2)) of 81 and 73 hours for R,R,R-alpha-tocopherol and all-rac-alpha-tocopherol, respectively. The t((1/2)) of tocotrienols is short, ranging from 3.8-4.4 hours for gamma- and alpha-tocotrienol, respectively. gamma-Tocopherol is degraded to 2, 7, 8-trimethyl-2-(beta-carboxyl)-6-hyrdoxychroman by the liver prior to renal elimination. Blood serum carotenoids in Western populations range from 0.28-0.52 micro mol/L for beta-carotene, from 0.2-0.28 for lutein, and from 0.29-0.60 for lycopene. All-trans-carotenoids have a better bioavailability than the 9-cis-forms. Elimination of carotenoids takes several days with a t((1/2)) of 5-7 and 2-3 days for beta-carotene and lycopene, respectively. The bioconversion of beta-carotene to retinal is dose-dependent, and ranges between 27% and 2% for a 6 and 126mg dose, respectively. Several oxidised metabolites of carotenoids are known. Flavonols such as quercetin glycosides and rutin are predominantly absorbed as aglycones, bound to plasma proteins and subsequently conjugated to glucuronide, sulfate, and methyl moieties. The t((1/2)) ranges from 12-19 hours. The bioavailabillity of catechins is low and they are eliminated with a t((1/2)) of 2-4 hours. Catechins are degraded to several gamma-valerolactone derivatives and phase II conjugates have also been identified. Only limited clinical pharmacokinetic data for other polyphenols such as resveratrol have been reported to date.

Fruit juice consumption modulates antioxidative status, immune status and DNA damage

Polyphenolic compounds exert a variety of physiological effects in vitro including antioxidative, immunomodulatory and antigenotoxic effects. In a randomized crossover study in healthy men on a low-polyphenol diet, we determined the effects of 2 polyphenol-rich juices (330 ml/d) supplemented for 2 weeks on bioavailability of polyphenols, markers of antioxidative and immune status, and reduction of DNA damage. Juices provided 236 mg (A) and 226 mg (B) polyphenols with cyanidin glycosides (A) and epigallocatechin gallate (B) as major polyphenolic ingredients. There was no accumulation of plasma polyphenols after two weeks of juice supplementation. In contrast, plasma malondialdehyde decreased with time during juice interventions. Moreover, juice consumption also increased lymphocyte proliferative responsiveness, with no difference between the two juices. Interleukin-2 secretion by activated lymphocytes and the lytic activity of natural killer cells were significantly increased by both juices. Juice intervention had no effect on single DNA strand breaks, but significantly reduced oxidative DNA damage in lymphocytes. A time-delay was observed between the intake of fruit juice and the reduction of oxidative DNA damage and the increase in interleukin-2 secretion. We conclude that consumption of either juice enhanced antioxidant status, reduced oxidative DNA damage and stimulated immune cell functions. However, fruit juice consumption for 2 weeks did not result in elevated plasma polyphenols in subjects after overnight fasting. Further studies should focus on the time-delay between juice intake and changes in measured physiological functions, as well as on active polyphenolic metabolites mediating the observed effects.