Inhibition of oncogene expression by green tea and (-)-epigallocatechin gallate in mice

Phytocompounds-based therapeutic approach: Investigating curcumin and green tea extracts on MCF-7 breast cancer cell line

BACKGROUND

Breast cancer (BC) has transcended lung cancer as the most common cancer in the world. Due to the disease's aggressiveness, rapid growth, and heterogeneity, it is crucial to investigate different therapeutic approaches for treatment. According to the World Health Organization (WHO), Plant-based therapeutics continue to be utilized as safe/non-toxic complementary or alternative treatments for cancer, even in developed countries, regardless of how cutting-edge conventional therapies are. Despite their low bioavailability, curcumin (CUR) and green tea (GT) represent safer therapeutic options. Due to their potent molecular-modulating properties on various cancer-related molecules and signaling pathways, they are considered gold-standard therapeutic agents and have been incorporated into the development of one or more therapeutic strategies of BC treatment.

METHODS

We investigated the modulatory role of CUR and GT extracts on significant multi molecular targets in MCF-7 BC cell line to assess their potential as BC multi-targeting agents. We analyzed the phytocompounds in GT leaves using High-performance liquid chromatography (HPLC) and Gas chromatography-mass spectrometry (GC-MS) techniques. The mRNA expression levels of Raf-1, Telomerase, Tumor necrosis factor alpha (TNF-α) and Interleukin-8 (IL-8) genes in MCF-7 cells were quantified using quantitative real-time PCR (qRT-PCR). The cytotoxicity of the extracts was assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and the released Lactate dehydrogenase (LDH), a valuable marker for identifying the programmed necrosis (necroptosis). Additionally, the concentrations of the necroptosis-related proinflammatory cytokines (TNF-α and IL-8) were measured using enzyme-linked immunosorbent assay (ELISA).

RESULTS

In contrast to the GT, the results showed the anticancer and cytotoxic properties of CUR against MCF-7 cells, with a relatively higher level of released LDH. The CUR extract downregulated the oncogenic Raf-1, suppressed the Telomerase and upregulated the TNF-α and IL-8 genes. Results from the ELISA showed a notable increase in IL-8 and TNF-α cytokines levels after CUR treatment, which culminated after 72 h.

CONCLUSIONS

Among both extracts, only CUR effectively modulated the understudy molecular targets, achieving multi-targeting anticancer activity against MCF-7 cells. Moreover, the applied dosage significantly increased levels of the proinflammatory cytokines, which represent a component of the cytokines-targeting-based therapeutic strategy. However, further investigations are recommended to validate this therapeutic approach.

Tea Drinking and the Risk of Carcinoma of the Urinary Bladder: A Meta-Analysis

Objective

For evaluation of the correlation between tea drinking and the risk of carcinoma of the urinary bladder.

Methods

By searching PubMed, Embase, and Cochrane Library databases, the original studies on tea drinking and carcinoma of the urinary bladder risk were collected, the data were extracted, and meta-analysis package 5.2-0 of R language was used for meta-analysis.

Results

This study contained 11 researches, composed of 7686 patients and 10320 controls. Tea drinking was not linked to carcinoma of the urinary bladder risk (OR:1.02, 95%CI: 0.95-1.11).

Conclusion

Tea drinking may not be linked to carcinoma of the urinary bladder, but more definitive results are needed from higher-quality trials.

Epigallocatechin-3-gallate augments the therapeutic effects of benzo[a]pyrene-mediated lung carcinogenesis

Our previous study found curcumin and vitamin E to have protective effects against benzo[a]pyrene (BaP) exposure in human normal lung epithelial BEAS-2B cells. The first objective of this study was to determine whether epigallocatechin-3-gallate (EGCG) elicited the same response. Co-treatment with 5 µM BaP and 20 µM EGCG in BEAS-2B promoted a significant reduction in cell viability and greater G2/M cell cycle arrest, induction of ROS, and reductions in BaP-induced CYP1A1/CYP1B1/COMT, EGFR, p-Akt (Ser473), p-p53 (Thr55), and survivin mRNA/protein expression, as well as an increase in p-p53 (Ser15). Based on these findings, the second objective was to extend the investigation by developing a novel BaP-transformed BEAS-2B cell line, BEAS-2B_BaP , to examine the effects of EGCG when co-administered with gefitinib, an EGFR tyrosine kinase inhibitor. Cell colony formation assay demonstrated in vitro tumorigenic potential of BEAS-2B_BaP , which had an overexpression of EGFR. Viability testing revealed gefitinib co-treatment with EGCG resulted in more cell death compared with gefitinib alone. Co-treated cells had greater reductions in gefitinib-induced CYP1A1/CYB1B1, EGFR, cyclin D1, p-Akt (Ser473), and survivin mRNA/protein expression, as well as an increase in p-p53 (Ser15). Therefore, EGCG was found to promote greater cytotoxicity to BEAS-2B co-treated with BaP and BEAS-2B_BaP upon gefitinib co-treatment through regulating metabolism enzymes and signaling pathways involving EGFR and p53. These findings suggest that EGCG did not act as a protective compound in BEAS-2B after acute BaP exposure, but has the potential to be a useful adjuvant chemotherapeutic compound when coupled with gefitinib for chemosensitization. © 2017 BioFactors, 43(4):529-539, 2017.

A Phase II Randomized, Double-blind, Presurgical Trial of Polyphenon E in Bladder Cancer Patients to Evaluate Pharmacodynamics and Bladder Tissue Biomarkers

We performed a phase II pharmacodynamic prevention trial of Polyphenon E [a green tea polyphenol formulation primarily consisting of epigallocatechin gallate (EGCG)] in patients prior to bladder cancer surgery. Patients with a bladder tumor were randomized to receive Polyphenon E containing either 800 or 1,200 mg of EGCG or placebo for 14 to 28 days prior to transurethral resection of bladder tumor or cystectomy. The primary objective was to compare the postintervention EGCG tissue levels in patients receiving Polyphenon E as compared with placebo. Secondary objectives included assessments of tissue expression of PCNA, MMP2, clusterin, VEGF, p27, IGF-1, IGFBP-3; correlation of tissue, plasma, and urine levels of EGCG; and EGCG metabolism by catechol-O-methyltransferase and UDP-glucuronosyltransferase pharmacogenomic mutations. Thirty-one patients (male:female, 26:5; mean age, 67.2 years) were randomized and 29 (94%) completed the study. There was not an observed significant difference (P = 0.12) in EGCG tissue levels between two Polyphenon E dosage groups combined versus placebo. However, a dose-response relationship for EGCG levels was observed in both normal (P = 0.046) and malignant bladder tissue (P = 0.005) across the three study arms. In addition, EGCG levels in plasma (P < 0.001) and urine (P < 0.001) increased and PCNA (P = 0.016) and clusterin (P = 0.008) were downregulated in a dose-dependent fashion. No pharmacogenomic relationship was observed. EGCG levels in plasma, urine, and bladder tissue followed a dose-response relationship, as did modulation of tissue biomarkers of proliferation and apoptosis. Despite the limitations of this pilot study, the observed pharmacodynamics and desirable biologic activity warrant further clinical studies of this agent in bladder cancer prevention. Cancer Prev Res; 10(5); 298-307. ©2017 AACR.

Implications of Green Tea and Its Constituents in the Prevention of Cancer via the Modulation of Cell Signalling Pathway

Green tea is commonly used as a beverage worldwide, especially in China, Japan, Morocco, and Saudi Arabia. Green tea and its constituents have been considered very effective in the prevention and treatment of various diseases. It contains a variety of catechins, which show a pivotal role in the modulation of biological activities and also act as chemopreventive agents. Earlier studies have confirmed that green tea and its chief constituent epigallocatechin gallate (EGCG) have a potential role in the management of cancer through the modulation of cell signaling pathways. In this review, we focused on the beneficial effects of green tea and its constituents in the cancer prevention and treatment and its impact on modulation of molecular pathways.

Green tea (Camelia sinensis) mediated suppression of IgE production by peripheral blood mononuclear cells of allergic asthmatic humans

Recent studies in our laboratory demonstrated the suppression of immunoglobulin E (IgE) production by green tea extract (GTE) in U266 cells. However, the effects of GTE or one of its components (EGCG) on IgE production by human peripheral blood mononuclear cells (PBMC) are unknown. PBMC (1.5 × 10⁶) obtained from serum IgE+, allergic asthmatic patients, were cultured ± GTE (1-100 ng/ml) or purified EGCG (0.5-50 ng/ml), and IgE levels were determined on day 10 by enzyme-linked immunosorbent assay (ELISA). High levels of IgE were detected in supernatants of the PBMC cultures on day 10. When GTE was included in vitro, IgE production by PBMC was suppressed on day 10, compared with control. Purified EGCG included in vitro also suppressed IgE production, but at lower levels, compared with control. This study demonstrates that GTE and its major catechin, EGCG, have immunoregulatory effects on human IgE responses.

Green Tea Polyphenol Epigallocatechin Gallate Inhibits Adipogenesis and Induces Apoptosis in 3T3-L1 Adipocytes

OBJECTIVE

Green tea catechins have been shown to promote loss of body fat and to inhibit growth of many cancer cell types by inducing apoptosis. The objective of this study was to determine whether epigallocatechin gallate (EGCG), the primary green tea catechin, could act directly on adipocytes to inhibit adipogenesis and induce apoptosis.

RESEARCH METHODS AND PROCEDURES

Mouse 3T3-L1 preadipocytes and mature adipocytes were used. To test the effect of EGCG on viability, cells were incubated for 3, 6, 12, or 24 hours with 0, 50, 100, or 200 microM EGCG. Viability was quantitated by MTS assay. To determine the effect of EGCG on apoptosis, adipocytes were incubated for 24 hours with 0 to 200 microM EGCG, then stained with annexin V and propidium iodide and analyzed by laser scanning cytometry. Both preadipocytes and adipocytes were also analyzed for apoptosis by terminal deoxynucleotidyl transferase dUTP nick-end labeling assay. To determine the effect of EGCG on adipogenesis, maturing preadipocytes were incubated during the 6-day induction period with 0 to 200 microM EGCG, then stained with Oil-Red-O and analyzed for lipid content.

RESULTS

EGCG had no effect on either viability or apoptosis of preconfluent preadipocytes. EGCG also did not affect viability of mature adipocytes; however, EGCG increased apoptosis in mature adipocytes, as demonstrated by both laser scanning cytometry and terminal deoxynucleotidyl transferase dUTP nick-end labeling assays. Furthermore, EGCG dose-dependently inhibited lipid accumulation in maturing preadipocytes.

DISCUSSION

These results demonstrate that EGCG can act directly to inhibit differentiation of preadipocytes and to induce apoptosis of mature adipocytes and, thus, could be an important adjunct in the treatment of obesity.

EGCG, green tea polyphenols and their synthetic analogs and prodrugs for human cancer prevention and treatment

Cancer-preventive effects of tea polyphenols, especially epigallocatechin-3-gallate (EGCG), have been demonstrated by epidemiological, preclinical, and clinical studies. Green tea polyphenols such as EGCG have the potential to affect multiple biological pathways, including gene expression, growth factor-mediated pathways, the mitogen-activated protein kinase-dependent pathway, and the ubiquitin/proteasome degradation pathway. Therefore, identification of the molecular targets of EGCG should greatly facilitate a better understanding of the mechanisms underlying its anticancer and cancer-preventive activities. Performing structure-activity relationship (SAR) studies could also greatly enhance the discovery of novel tea polyphenol analogs as potential anticancer and cancer-preventive agents. In this chapter, we review the relevant literature as it relates to the effects of natural and synthetic green tea polyphenols and EGCG analogs on human cancer cells and their potential molecular targets as well as their antitumor effects. We also discuss the implications of green tea polyphenols in cancer prevention.

Polyphenols and cancer cell growth

Polyphenols constitute an important group of phytochemicals that gained increased research attention since it was found that they could affect cancer cell growth. Initial evidence came from epidemiologic studies suggesting that a diet that includes regular consumption of fruits and vegetables (rich in polyphenols) significantly reduces the risk of many cancers. In the present work we briefly review the effects of polyphenols on cancer cell fate, leading towards growth, differentiation and apoptosis. Their action can be attributed not only to their ability to act as antioxidants but also to their ability to interact with basic cellular mechanisms. Such interactions include interference with membrane and intracellular receptors, modulation of signaling cascades, interaction with the basic enzymes involved in tumor promotion and metastasis, interaction with oncogenes and oncoproteins, and, finally, direct or indirect interactions with nucleic acids and nucleoproteins. These actions involve almost the whole spectrum of basic cellular machinery--from the cell membrane to signaling cytoplasmic molecules and to the major nuclear components--and provide insights into their beneficial health effects. In addition, the actions justify the scientific interest in this class of compounds, and provide clues about their possible pharmaceutical exploitation in the field of oncology.

Medicinal Benefits of Green Tea: Part II. Review of Anticancer Properties

Currently there is wide interest in the medicinal benefits of green tea (Camellia sinensis). Tea is one of the most widely consumed beverages in the world, and extracts of tea leaves are also sold as dietary supplements. Green tea extracts contain a unique set of catechins that possess biologic activity in antioxidant, antiangiogenesis, and antiproliferative assays that are potentially relevant to the prevention and treatment of various forms of cancer. With the increasing interest in the health properties of tea and a significant rise in their scientific investigation, it is the aim of this review to summarize recent findings on the anticancer and medicinal properties of green tea, focusing on the biologic properties of the major tea catechin, (-)-epigallocatechin and its antitumor properties.

Effect of green tea extract on the induction of ornithine decarboxylase and the activation of extracellular signal-regulated kinase in bladder carcinoma ECV304 cells

According to several studies, green tea and individual catechins can inhibit the induction of ornithine decarboxylase (ODC), the key enzyme in the biosynthesis of polyamines. It has been suggested that the inhibition of ODC induction may offer an explanation to the anticancer and chemopreventive activities of green tea. In the present study, however, treatment of bladder carcinoma ECV304 cells with green tea extract (GTE) was not able to reduce the induction of ODC by fetal calf serum. Actually, in the absence of serum, GTE provoked a dose-dependent and remarkable induction of ODC activity. The induction of ODC, which could be elicited also by (-)-epigallocatechin 3-gallate, a major green tea component, required an early activation of extracellular signal-regulated kinase 1 and 2 (ERK), and both events appeared to be dependent on an alteration of the status of cellular thiol groups. Pretreatment with specific ERK or ODC inhibitors was able to prevent a late caspase activation but hardly affected the loss of cell viability provoked by GTE. In conclusion, to our knowledge, this is the first study showing that GTE can promote ODC induction in a tumor cell line.

Inhibition of phorbol ester-induced COX-2 expression by epigallocatechin gallate in mouse skin and cultured human mammary epithelial cells

Green tea polyphenols are reported to possess substantial antiinflammatory and chemopreventive properties. However, the molecular mechanism of chemopreventive activity of green tea polyphenols is not fully understood. An abnormally elevated level of cyclooxygenase-2 (COX-2) is implicated in the pathogenesis of carcinogenesis. In the present study, we found that pretreatment of the green tea extract enriched with catechin and epigallocatechin gallate (EGCG) by gavage inhibited COX-2 expression induced by the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) in mouse skin. Similarly, EGCG downregulated COX-2 in TPA-stimulated human mammary epithelial cells (MCF-10A) in culture. To further elucidate the underlying mechanism of COX-2 inhibition by green tea extract and EGCG, we examined their effects on the activation of extracellular signal-regulated protein kinase (ERK) and p38 mitogen-activated protein kinase (MAPK), which are upstream enzymes known to regulate COX-2 expression in many cell types. Pretreatment with EGCG as well as green tea extract caused a decrease in the activation of ERK. In addition, EGCG inhibited the catalytic activity of ERK and p38 MAPK, suggesting that these signal-transducing enzymes could be potential targets for previously reported antitumor promoting activity of EGCG.

Effect of Increased Tea Consumption on Oxidative DNA Damage among Smokers: A Randomized Controlled Study

Tea drinking has been associated with decreased occurrence of cancer and heart disease. One potential mechanism for these findings is the strong antioxidant effect of tea polyphenols. A phase II randomized controlled tea intervention trial was designed to study the effect of high consumption (4 cups/d) of decaffeinated green or black tea on oxidative DNA damage as measured by urinary 8-hydroxydeoxyguanosine (8-OHdG) among smokers over a 4-mo period. A total of 143 heavy smokers, aged 18-79 y, were randomized to drink either green or black tea or water. Levels of plasma and urinary catechins and urinary 8-OHdG were measured monthly. A total of 133 of 143 smokers completed the 4-mo intervention. Multiple linear regression models were used to estimate the main effects and interaction effect of green and black tea consumption on creatinine-adjusted urinary 8-OHdG, with or without adjustment for potential confounders. Plasma and urinary levels of catechins rose significantly in the green tea group compared with the other two groups. Assessment of urinary 8-OHdG after adjustment for baseline measurements and other potential confounders revealed a highly significant decrease in urinary 8-OHdG (-31%) after 4 mo of drinking decaffeinated green tea (P = 0.002). No change in urinary 8-OHdG was seen among smokers assigned to the black tea group. These data suggest that regular green tea drinking might protect smokers from oxidative damages and could reduce cancer risk or other diseases caused by free radicals associated with smoking.

Molecular mechanisms underlying chemopreventive activities of anti-inflammatory phytochemicals: down-regulation of COX-2 and iNOS through suppression of NF-kappa B activation

A wide array of phenolic substances, particularly those present in edible and medicinal plants, have been reported to possess substantial anticarcinogenic and antimutagenic activities. The majority of naturally occurring phenolics retain antioxidative and anti-inflammatory properties which appear to contribute to their chemopreventive or chemoprotective activity. Cyclooxygenase-2 (COX-2) inducible and nitric oxide synthase (iNOS) are important enzymes that mediate inflammatory processes. Improper up-regulation of COX-2 and/or iNOS has been associated with pathophysiology of certain types of human cancers as well as inflammatory disorders. Since inflammation is closely linked to tumor promotion, substances with potent anti-inflammatory activities are anticipated to exert chemopreventive effects on carcinogenesis, particularly in the promotion stage. Examples are curcumin, a yellow pigment of turmeric (Curcuma longa L., Zingiberaceae), the green tea polyphenol epigallocatechin gallate (EGCG), and resveratrol from grapes (Vitis vinifera, Vitaceae) that strongly suppress tumor promotion. Recent studies have demonstrated that eukaryotic transcription factor nuclear factor-kappa B (NF-kappa B) is involved in regulation of COX-2 and iNOS expression. Several chemopreventive phytochemicals have been shown to inhibit COX-2 and iNOS expression by blocking improper NF-kappa B activation. Multiple lines of compelling evidence indicate that extracellular-regulated protein kinase and p38 mitogen-activated protein kinase are key elements of the intracellular signaling cascades responsible for NF-kappa B activation in response to a wide array of external stimuli. Curcumin, EGCG and resveratrol have been shown to suppress activation of NF-kappa B. One of the plausible mechanisms underlying inhibition of NF-kappa B activation by aforementioned phytochemicals involves repression of degradation of the inhibitory unit I kappa B alpha, which hampers subsequent nuclear translocation of the functionally active subunit of NF-kappa B.

Prevention of carcinogenesis by tea polyphenols

Tea, an extract of the leaves of the plant Camellia sinensis, has been considered a medicine and healthful beverage for ages. The beneficial effects of tea are thought to be due to its polyphenolic components. Herein, we discuss the present status of tea as a possible cancer chemopreventive agent, covering basic chemistry and biochemical activity of tea, pharmacokinetics of major tea components, studies in animal and cell lines, epidemiological investigations, and future challenges. Tea is one of the few chemopreventive agents known to have protective effects at different stages of the carcinogenic process. Tea constituents may inhibit this process by modulating signal transduction pathways leading to the inhibition of cell proliferation and transformation and enhancement of apoptosis. These activities may or may not be due to the antioxidative activity of tea polyphenols. The bioavailability and tissue levels of tea polyphenols is a key topic to be studied in order to understand the mechanisms of action of tea and its possible protection against cancer in humans.

Green tea and its major components ameliorate immune dysfunction in mice bearing Lewis lung carcinoma and treated with the carcinogen NNK

The protective effects of tea and/or its components on dysfunction of immune functions during tumor growth and carcinogenesis in mice were studied using two experimental models: C57/BL6J mice transplanted with Lewis lung carcinoma (LLC) and Kunming mice treated with a single dose of 4-(methylnitrosamino-)-1-(3-pyridyl)-1-butanone (NNK). In C57/BL6J mice bearing LLC, the weight of the thymus decreased, the proportion of CD4(+)-positive T lymphocytes and the ratio of CD4+ to CD8+ decreased, luminol-enhanced chemiluminescence of white blood cells in peripheral blood stimulated by zymosan increased, and plaque-forming cells (PFC) decreased. However, in LLC-bearing mice given green tea as drinking water, all immune functions were improved, along with inhibition of tumor growth. In Kunming mice treated with NNK, during the four weeks of observation, their immunologic indicators, such as phagocytosis of macrophages in the abdominal cavity, luminol-enhanced chemiluminescence of white blood cells, plaque-forming cells, and delayed-type hypersensitivity, increased or decreased to various extents compared with normal controls. However, these changes were significantly prevented in the mice given green tea, mixed tea, or tea polyphenol as drinking water. In conclusion, tea and its components ameliorated immune dysfunction in mice bearing LLC or treated with the carcinogen NNK.

Molecular mechanisms of chemopreventive effects of selected dietary and medicinal phenolic substances

Recently, considerable attention has been focused on identifying naturally occurring chemopreventive substances capable of inhibiting, retarding, or reversing the multi-stage carcinogenesis. A wide array of phenolic substances, particularly those present in dietary and medicinal plants, have been reported to possess substantial anticarcinogenic and antimutagenic activities. The majority of these naturally occurring phenolics retain antioxidative and anti-inflammatory properties which appear to contribute to their chemopreventive or chemoprotective activity. Capsaicin (trans-8-methyl-N-vanillyl-6-nonenamide), a pungent ingredient of hot chili pepper, protects against experimentally-induced mutagenesis and tumorigenesis. It also induces apoptosis in various immortalized or malignant cell lines. Plants of ginger family (Zingiberaceae) have been frequently and widely used as spices and also, in traditional oriental medicine. Curcumin, a yellow ingredient from turmeric (Curcuma longa L., Zingiberaceae), has been extensively investigated for its cancer chemopreventive potential. Yakuchinone A [1-(4'-hydroxy-3'-methoxyphenyl)-7-phenyl-3-heptanone] and yakuchinone B [1-(4'-hydroxy-3'-methoxyphenyl)-7-phenylhept-1-en-3-one] present in Alpinia oxyphylla Miquel (Zingiberaceae) have inhibitory effects on phorbol ester-induced inflammation and skin carcinogenesis in mice, and oxidative stress in vitro. These diarylheptanoids suppress phorbol ester-induced activation of ornithine decarboxylase and production of tumor necrosis factor-alpha or interleukin-1alpha and their mRNA expression. They also nullified the phorbol ester-stimulated induction of activator protein 1 (AP-1) in cultured human promyelocytic leukemia (HL-60) cells. In addition, both yakuchinone A and B induced apoptotic death in HL-60 cells. Ginger (Zingiber officinale Roscoe, Zingiberaceae) contains such pungent ingredients as [6]-gingerol and [6]-paradol, which also have anti-tumor promotional and antiproliferative effects. Resveratrol (3, 5,4'-trihydroxy-trans-stilbene), a phytoalexin found in grapes and other dietary and medicinal plants, and (-)-epigallocatechin gallate, a major antioxidative green tea polyphenol, exert striking inhibitory effects on diverse cellular events associated with multi-stage carcinogenesis. In addition, these compounds have ability to suppress proliferation of human cancer cells via induction of apoptosis.

(+)-Catechin prevents human plasma oxidation

Based on the recognized capacity of (+)-catechin (CTCH) to prevent free radical-mediated damage in different biological systems, its role in the protection of human plasma from oxidation was investigated. Samples of human blood plasma were incubated with 50 mM AAPH [2,2'-azobis-(2-amidinopropane) clorhidrate] or AMVN [2,2'-azobis(2,4-valeronitrile)], in the absence or the presence of CTCH (0.01 to 1 mM). Lipid oxidation was evaluated measuring the formation of 2-thiobarbituric acid reactive substances (TBARS). Alpha-tocopherol (AT), beta-carotene (BC), and CTCH were measured by reverse phase HPLC with electrochemical detection. TBARS formation was dependent on incubation time and on the nature of the azocompound, yielding 4.8 +/- 0.9, and 14.9 +/- 3.4 microM MDA, after 4 h, in AAPH and AMVN-exposed plasma, respectively. Plasma AT and BC were extensively depleted under these oxidant conditions. The addition of CTCH prevented or delayed the formation of TBARS, and the depletion of AT and BC in a dose dependent manner. This antioxidant effect was dependent on the concentration of CTCH and on the physical characteristics of the radical initiator. CTCH supplementation modified not only the lag time for the antioxidants depletion, but also the consumption rate. These results indicate that CTCH was an effective antioxidant in human blood plasma, delaying the consumption of endogenous lipid soluble antioxidants (AT and BC) and inhibiting lipid oxidation.

Lignan and isoflavonoid concentrations in tea and coffee

Tea is a beverage consumed widely throughout the world. The existence in tea of chemopreventing compounds possessing antimutagenic, anticarcinogenic and antioxidative properties has been reported. High intakes of tea and foods containing flavonoids have recently been shown to be negatively correlated to the occurrence of CHD. However, tea may contain other compounds with similar activities. Using a new gas chromatographic-mass spectrometric method we measured lignans and isoflavonoids in samples of twenty commercial teas (black, green and red varieties) and, for comparison, six coffees. Both unbrewed and brewed tea were investigated. The analysis of the teas yielded relatively high levels of the lignans secoisolariciresinol (5.6-28.9 mg/kg; 15.9-81.9 mumol/kg) and matairesinol (0.56-4.13 mg/kg; 1.6-11.5 mumol/kg) but only low levels of isoflavonoids. Because the plant lignans, as well as their mammalian metabolites enterolactone and enterodiol, have antioxidative properties and these mammalian lignans occur in high concentrations in plasma, we hypothesize that lignan polyphenols may contribute to the protective effect of tea on CHD.