GREEN TEA



Table of Contents

image Cancer-preventive effects of drinking green tea among a Japanese population
image Green tea extract inhibits nucleoside transport and potentiates the antitumor effect of antimetabolites
image Cross sectional study of effects of drinking green tea on cardiovascular and liver diseases
image Green tea epigallocatechin gallate shows a pronounced growth inhibitory effect on cancerous cells but not on their normal counterparts
image Possible contribution of green tea drinking habits to the prevention of stroke
image Polyphenols as cancer chemopreventive agents.
image Protective effect of tea polyphenol on rat myocardial injury induced by isoproterenol
image Effect of tea polyphenols on glucan synthesis by glucosyltransferase from Streptococcus mutans.
image Inhibition of tobacco-specific nitrosamine-induced lung tumorigenesis in A/J mice by green tea and its major polyphenol as antioxidants.
image Oxidation of caffeine and related methylxanthines in ascorbate and polyphenol-driven Fenton-type oxidations.
image Green and black tea consumption by humans: impact on polyphenol concentrations in feces, blood and urine.
image Inhibitory effects and toxicity of green tea polyphenols for gastrointestinal carcinogenesis
image Effect of green tea on N-butyl-N-(4-hydroxybutyl) nitrosamine-induced urinary bladder carcinogenesis in rats
image Inhibitory effect of six green tea catechins and caffeine on the growth of four selected human tumor cell lines
image Prevention of ornithine decarboxylase induction in Ehrlich ascites tumor cells by tea polyphenols
image Prevention of photocarcinogenesis by topical administration of pure epigallocatechin gallate isolated from green tea
image Natural antimutagenic agents may prolong efficacy of human immunodeficiency virus drug therapy
image Prevention of photocarcinogenesis by topical administration of pure epigallocatechin gallate isolated from green tea
image Chemopreventive effects of green and black tea on pulmonary and hepatic carcinogenesis
image Nutrition and esophageal cancer

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Cancer-preventive effects of drinking green tea among a Japanese population

Imai K, Suga K, Nakachi K Department of Epidemiology, Saitama Cancer Center Research Institute, Japan.

Prev Med 1997 Nov-Dec;26(6):769-75
BACKGROUND: Laboratory studies have revealed the cancer preventive effects of green tea, so the association between green tea consumption and cancer was examined in a human population. METHODS: The association between green tea consumption and cancer incidence was studied in our prospective cohort study of a Japanese population. We surveyed 8,552 individuals over 40 years of age living in a town in Saitama prefecture on their living habits, including daily consumption of green tea. During the 9 years of follow-up study (71,248.5 person-years), we identified a total of 384 cases of cancer in all sites. RESULTS: We found a negative association between green tea consumption and cancer incidence, especially among females drinking more than 10 cups a day. The slowdown in increase of cancer incidence with age observed among females who consumedmore than 10 cups a day is consistent with the finding that increased consumption of green tea is associated with later onset of cancer. Age-standardized average annual incidence rate was significantly lower among females who consumed large amounts of green tea. Relative risk (RR) of cancer incidence was also lower among both females (RR = 0.57, 95% CI = 0.33-0.98) and males (RR = 0.68, 95% CI = 0.39-1.21) in groups with the highest consumption, although the preventive effects did not achieve statistical significance among males, even when stratified by smoking and adjusted for alcohol and dietary variables. CONCLUSION: Our epidemiological study showed that green tea has a potentially preventive effect against cancer among humans.

Green tea extract inhibits nucleoside transport and potentiates the antitumor effect of antimetabolites

Zhen Y, Cao S, Xue Y, Wu S Institute of Medical Biotechnology, CAMS, Beijing.

Chin Med Sci J 1991 Mar;6(1):1-5
The present study provides evidence that green tea extract (GTE), consisting of polyphenol components, is a highly active nucleoside transport inhibitor. GTE markedly inhibited radiolabeled thymidine and uridine transport in mouse leukemia L1210 cells, with IC50 values of 3.2 and 8.0 mumol/L, respectively. GTE blocked the rescue effect of exogenous nucleosides and enhanced the cytotoxicity of AraC and MTX to L1210 cells and human hepatoma BEL-7402 cells. GTE markedly potentiated the inhibitory effect of AraC on leukemia L1210 and P388 in mice. These results indicate that GTE is potentially useful when combined with antimetabolites in cancer chemotherapy.

Cross sectional study of effects of drinking green tea on cardiovascular and liver diseases

Imai K, Nakachi K Department of Epidemiology, Saitama Cancer Center Research Institute, Japan.

BMJ 1995 Mar 18;310(6981):693-6
OBJECTIVE: To investigate the association between consumption of green tea and various serum markers in a Japanese population, with special reference to preventive effects of green tea against cardiovascular disease and disorders of the liver. DESIGN: Cross sectional study. SETTING: Yoshimi, Japan. SUBJECTS: 1371 men aged over 40 years resident in Yoshimi and surveyed on their living habits including daily consumption of green tea. Their peripheral blood samples were subjected to several biochemical assays. RESULTS: Increased consumption of green tea was associated with decreased serum concentrations of total cholesterol (P for trend < 0.001) and triglyceride (P for trend = 0.02) and an increased proportion of high density lipoprotein cholesterol together with a decreased proportion of low and very low lipoprotein cholesterols (P for trend = 0.02), which resulted in a decreased atherogenic index (P for trend = 0.02). Moreover, increased consumption of green tea, especially more than 10 cups a day, was related to decreased concentrations of hepatological markers in serum, aspartate aminotransferase (P for trend = 0.06), alanine transferase (P for trend = 0.07), and ferritin (P for trend = 0.02). CONCLUSION--The inverse association between consumption of green tea and various serum markers shows that green tea may act protectively against cardiovascular disease and disorders of the liver.

Green tea epigallocatechin gallate shows a pronounced growth inhibitory effect on cancerous cells but not on their normal counterparts

Chen ZP, Schell JB, Ho CT, Chen KY Department of Chemistry, Rutgers, The State University of New Jersey, Piscataway 08855-0939, USA.

Cancer Lett 1998 Jul 17;129(2):173-9
(-)-Epigallocatechin gallate (EGCG), a catechin polyphenol compound, represents the main ingredient of green tea extract. Although EGCG has been shown to be growth inhibitory in a number of tumor cell lines, it is not clear whether the effect is cancer-specific. In this study we compared the effect of EGCG on the growth of SV40 virally transformed WI38 human fibroblasts (WI38VA) with that of normal WI38 cells. The IC50 value of EGCG was estimated to be 120 and 10 microM for WI38 and WI38VA cells, respectively. Thus, EGCG at 40 microM completely inhibited the growth of WI38VA cells, but had little or no inhibitory effect on the growth of WI38 cells. Similar differential growth inhibition was also observed between a human colorectal cancer cell line (Caco-2), a breast cancer cell line (Hs578T) and their respective normal counterparts. EGCG at a concentration range of 40-200 microM induced a significant amount of apoptosis in WI38VA cultures, but not in WI38 cultures, as determined by terminal deoxynucleotidyl transferase assay. After exposure to EGCG at 200 microM for 8 h, more than 50% of WI38VA cells in a confluent culture became apoptotic. In contrast, less than 1% of WI38 cells displayed apoptotic labeling under the same condition. EGCG did not affect the serum-induced expression of c-fos and c-myc genes in normal WI38 cells. However, it significantly enhanced their expression in transformed W138VA cells. It is possible that differential modulation of certain genes, such as c-fos and c-myc, may cause differential effects of EGCG on the growth and death of cancer cells.

Possible contribution of green tea drinking habits to the prevention of stroke

Sato Y, Nakatsuka H, Watanabe T, Hisamichi S, Shimizu H, Fujisaku S, Ichinowatari Y, Ida Y, Suda S, Kato K, et al Department of Environmental Health, Tohoku University School of Medicine, Sendai, Japan.

Tohoku J Exp Med 1989 Apr;157(4):337-43
Among 5910 nondrinking and nonsmoking women (of greater than or equal to 40 years of age) in a prefectural city of Sendai, and two villages of Taijiri and Wakuya in Miyagi prefecture, Japan, medical history of stroke was less frequently observed among those who took more green tea in daily life. No relation with tea drinking was observed for hypertension history. The uneven distribution of stroke history was detectable even after the effects of age, location of residence, and high salt intake were ruled out. The incidence of stroke and cerebral hemorrhage during a 4-year follow-up of the study population was twice or more times higher in those who took less green tea (less than 5 cups a day) than in those who took more (greater than or equal to 5 cups daily).

Polyphenols as cancer chemopreventive agents.

J Cell Biochem Suppl (UNITED STATES) 1995, 22 p169-80
This article summarizes available data on the chemopreventive efficacies of tea polyphenols, curcumin and ellagic acid in various model systems. Emphasis is placed upon the anticarcinogenic activity of these polyphenols and their proposed mechanism(s) of action. Tea is grown in about 30 countries and, next to water, is the most widely consumed beverage in the world. Tea is manufactured as either green, black, or oolong; black tea represents approximately 80% of tea products. Epidemiological studies, though inconclusive, suggest a protective effect of tea consumption on human cancer. Experimental studies of the antimutagenic and anticarcinogenic effects of tea have been conducted principally with green tea polyphenols (GTPs). GTPs exhibit antimutagenic activity in vitro, and they inhibit carcinogen-induced skin, lung, forestomach, esophagus, duodenum and colon tumors in rodents. In addition, GTPs inhibit TPA-induced skin tumor promotion in mice. Although several GTPs possess anticarcinogenic activity, the most active is (-)-epigallocatechin-3-gallat e (EGCG), the major constituent in the GTP fraction. Several mechanisms appear to be responsible for the tumor-inhibitory properties of GTPs, including enhancement of antioxidant (glutathione peroxidase, catalase and quinone reductase) and phase II (glutathione-S-transferase) enzyme activities; inhibition of chemically induced lipid peroxidation; inhibition of irradiation- and TPA-induced epidermal ornithine decarboxylase (ODC) and cyclooxygenase activities; inhibition of protein kinase C and cellular proliferation; antiinflammatory activity; and enhancement of gap junction intercellular communication. Curcumin is the yellow coloring agent in the spice tumeric. It exhibits antimutagenic activity in the Ames Salmonella test and has anticarcinogenic activity, inhibiting chemically induced preneoplastic lesions in the breast and colon and neoplastic lesions in the skin, forestomach, duodenum and colon of rodents. In addition, curcumin inhibits TPA-induced skin tumor promotion in mice. The mechanisms for the anticarcinogenic effects of curcumin are similar to those of the GTPs. Curcumin enhances glutathione content and glutathione-S-transferase activity in liver; and it inhibits lipid peroxidation and arachidonic acid metabolism in mouse skin, protein kinase C activity in TPA-treated NIH 3T3 cells, chemically induced ODC and tyrosine protein kinase activities in rat colon, and 8-hydroxyguanosine formation in mouse fibroblasts. Ellagic acid is a polyphenol found abundantly in various fruits, nuts and vegetables. Ellagic acid is active in antimutagenesis assays, and has been shown to inhibit chemically induced cancer in the lung, liver, skin and esophagus of rodents, and TPA-induced tumor promotion in mouse skin.

Protective effect of tea polyphenol on rat myocardial injury induced by isoproterenol

Chinese Traditional and Herbal Drugs (China)(Apr) 1995
The ability of tea polyphenol to protect against myocardial injury induced by isoproterenol was studied in rats. Pretreatment with 10 mg/kg intraperitoneal tea polyphenol 5 days before isoproterenol administration decreased malonyldehyde concentration, and creatine phosphokinase and lactic dehydrogenase activities, and inhibited the extent of myocardial injury similar to the action of propranolol. Plasma renin activity was also decreased.

Effect of tea polyphenols on glucan synthesis by glucosyltransferase from Streptococcus mutans.

Chem Pharm Bull (Tokyo) (JAPAN) Mar 1990, 38 (3)
In the course of our studies on the development of anti-plaque agents for prevention of dental caries, we investigated effects of some of tea preparations and their individual components on the glucan synthesis catalyzed by glucosyltransferase (GTF) from Streptococcus mutans. Extracts of green tea and black tea, and polyphenol mixtures showed appreciable inhibition in the synthesis of insoluble glucan. Among the components isolated from tea infusions, theaflavin and its mono- and digallates had potent inhibitory activities at concentrations of 1-10 mM against GTF. (+)-Catechin, (-)-epicatechin and their enantiomers had moderate inhibitory activities at these concentrations, while galloyl esters of (-)-epicatechin, (-)-epigallocatechin and (-)-gallocatechin had increased inhibitory activities. Study on feasibility of Chinese green tea polyphenols (CTP) for preventing dental caries]

Inhibition of tobacco-specific nitrosamine-induced lung tumorigenesis in A/J mice by green tea and its major polyphenol as antioxidants.

Xu Y, Ho CT, Amin SG, Han C, Chung FL

Cancer Res 1992 Jul 15;52(14):3875-9
In this study we examined the effects of green tea and its major components, (-)-epigallocatechin gallate (EGCG) and caffeine, on the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1- butanone (NNK)-induced lung tumorigenesis in A/J mice. We also studied the effects of green tea and EGCG on O6-methylguanine and 8- hydroxydeoxyguanosine (8-OH-dGuo) formation in lung tissues caused by NNK treatment. Mice were given 2% tea, 560 ppm EGCG, or 1120 ppm caffeine in drinking water for 13 weeks. During this time, NNK (11.65 mg/kg body weight) was administered by gavage three times weekly for 10 weeks from weeks 3 to 12. The bioassay was terminated 6 weeks after the last NNK treatment. Mice treated with NNK developed 22.5 lung adenomas per mouse, whereas NNK-treated mice that drank green tea or EGCG as drinking water developed only 12.2 (P less than 0.01) and 16.1 (P less than 0.05) tumors per mouse, respectively. Mice that drank green tea or caffeine solution showed lower body weight gains, although little difference in water and diet consumption was noted in these groups. While green tea and EGCG exerted little effect on the formation of O6-methylguanine, a critical DNA lesion in NNK lung tumorigenesis, both treatments suppressed the increase of 8-OH-dGuo levels in mouse lung DNA. The inhibition of 8-OH-dGuo formation in lung DNA by green tea and EGCG is consistent with their ability to inhibit lung tumorigenesis by NNK. Because 8-OH-dGuo is a DNA lesion caused by oxidative damage, these results suggest that the mechanism of inhibition by green tea and EGCG in NNK-induced lung tumorigenesis is due at least partly to their antioxidant properties.

Oxidation of caffeine and related methylxanthines in ascorbate and polyphenol-driven Fenton-type oxidations.

Stadler RH,. Richoz J, Turesky RJ, Welti DH, Fay LB

Free Radic Res 1996 Mar;24(3):225-10
Caffeine and related methylxanthines were subjected to free radical mediated oxidation by incubation with Fe(3+)-EDTA/ascorbate and Fe(3+)-EDTA/polyphenolics. The reaction mixtures were analysed by reverse-phase HPLC, revealing the corresponding C-8 hydroxylated analogues as the major products of hydroxyl radical mediated attack. Further oxidation products of caffeine, analysed by liquid chromatography-mass spectrometry (LC-MS), were the N1-, N3- and N7- demethylated methylxanthine analogues theobromine, paraxanthine and theophylline, respectively. Isolable amounts of the imidazole ring operated 6-amino-5-(N-formylmethyl-amino)-1,3-dimethyl-uracil (1,3,7- DAU) derivative were also detected, which was characterised by 1H NMR and mass spectroscopy. The identified products indicate that the pertinent chemical reactions, i.e. C-8 hydroxylation, demethylations, and C8-N9 bond scission, are comparable to the primary metabolic pathways of caffeine in humans. The influence of pH, transition metals, hydrogen peroxide, free radical scavengers and metal chelators on caffeine oxidation was studied. This report illustrates that natural food-borne reactants can aid in identifying specific chemical markers of free radical induced damage. Furthermore, potentially anti-and pro-oxidative reactions can be elucidated which may be important in assessing the impact of nutrient additives and supplements on the shelf life and stability of foods and beverages.

Green and black tea consumption by humans: impact on polyphenol concentrations in feces, blood and urine.

He YH, Kies C

Plant Foods Hum Nutr 1994 Oct;46(3):221-9
The objective of the study was to determine the effects of green tea, black tea and decaffeinated black tea consumption on urinary and fecal excretions and whole blood and blood serum concentrations of polyphenols. The 56 day study was divided into four randomly arranged experimental periods of 14 days each during which the 10 healthy adult subjects consumed a laboratory controlled, constant, measured diet based on ordinary foods. During separate periods, subjects received no tea, green tea, regular black tea or decaffeinated black tea beverages at the three daily meals. Subjects made complete collections of urine and stools throughout the study and fasting blood samples were drawn at the beginning of the study and at the end of each experimental period. Polyphenols contained in urine, feces, whole blood, blood serums, food and tea were analyzed by the spectrophotometry method of Wah Lau et al. (1989). Green tea consumption resulted in highest intakes in greatest fecal and urinary excretions, highest retentions, and high whole blood concentrations of polyphenols followed by effects of regular black tea, decaffeinated black tea and no tea treatments. These results indicate that polyphenols from tea are at least partly absorbable. Hence, both positive and negative effects of dietary polyphenol may occur internal to the body proper and not only as effects within the intestines.

Inhibitory effects and toxicity of green tea polyphenols for gastrointestinal carcinogenesis

Cancer (USA) , 1996, 77/8 SUPPL. (1662-1667)
BACKGROUND. Recently, an epidemiologic study showed a lower risk of gastrointestinal carcinogenesis in green tea drinkers. An experiment on two stage skin carcinogenesis in mice showed that (-)-epigallocatechin gallate (EGCG), one of the main constituents of green tea, inhibited tumor formation. METHODS.The inhibitory effects of EGCG and green tea extract (GTE) on N-ethyl-N'-nitro-N nitrosoguanidine (ENNG)-induced duodenal carcinogenesis in the mouse, N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)-induced carcinogenesis of the glandular stomach in the rat, and azoxymethane induced colon carcinogenesis in the rat were examined. The toxicity of GTE was assessed experimentally and GTE was applied clinically in normal volunteers to determine the effective dose and to assess its harmful effects. RESULTS: EGCG and GTE inhibited chemical carcinogenesis of ts. Judging from the epidemiologic and experimental findings, it was determined that 1 g per day of GTE might be an effective dose. GTE was not toxic and no harmful effect was found during its clinical use. CONCLUSIONS. These findings suggest that EGCG and GTE are useful in preventing gastrointestinal carcinogenesis, and the clinical usefulness of GTE, which has no harmful effects and is inexpensive, should be studied further.

Effect of green tea on N-butyl-N-(4-hydroxybutyl) nitrosamine-induced urinary bladder carcinogenesis in rats

Journal of the Medical Society of Toho University (Japan) , 1996, 42/6 (642-645)
The effect of green tea on N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN)-induced urinary bladder carcinogenesis in rats was investigated. Fifty male WISTAR rats, seven weeks of age, were divided into two groups and BBN was added to their drinking water with a concentration of 0.05% for 5 weeks. The drinking water was then replaced with tap water for the control group and green tea for the green tea group. All rats were sacrificed at 40 weeks. Regarding the mean volume per tumor, there was significant difference between both groups. However, there was no significant difference between both groups in the number of rats with carcinomas and the number of tumors per rat. The body weightgroups and no side effects were noted. These results indicate that oral administration of green tea suppresses the growth of urinary bladder tumors in rats induced by BBN.

Inhibitory effect of six green tea catechins and caffeine on the growth of four selected human tumor cell lines

Anti-Cancer Drugs (United Kingdom) , 1996, 7/4 (461-468)
Green tea is air aqueous infusion of dried unfermented leaves of Camellia sinensis (family Theaceae) from which numerous biological activities have been reported including antimutagenic, antibacterial, hypocholesterolemic, antioxidant, antitumor and cancer preventive activities. From the aqueous-alcoholic extract of green tea leaves, six compounds (+)-gallacatechin (GC), (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECG), (-)-epigallocatechin gatlate (EGCG) and caffeine, were isolated and purified. Together with (+)-catechin, these compounds were tested against each of four human tumor cell lines (MCF-7 breast carcinoma, HT-29 colon carcinoma, A-427 lung carcinoma and UACC-375 melanoma). The three most potent green tea components against all four tumor cell lines were EGCG, GC and EGG. EGCG was the most potent of the seven green tea components against three out of the four cell lines (i.e. MCF-7 breast cancer, HT-29 colon cancer and UACC-375 melanoma). On the basis of these extensive in vitro studies, it would be of considerable interest to evaluate all three of these components in comparative preclinical in vivo animal tumor model systems before final decisions are made concerning which of these potential chemopreventive drugs should be taken into broad clinical trials.

Prevention of ornithine decarboxylase induction in Ehrlich ascites tumor cells by tea polyphenols

Cancer Journal (France) , 1996, 9/3 (161-167)
Green tea extract and some components of green tea are known to inhibit carcinogenesis. However, the mechanisms by which green tea extract exerts its anticarcinogenic effect are not yet clearly understood. We have examined the effect of tea polyphenols on polyamine metabolism and the mechanism of its antitumor activity in Ehrlich ascites tumor cells. Ornithine decarboxylase (ODC) activity was measured by estimating the release of 14CO2 from L(1- 14C) ornithine. The amount of ODC mRNA was measured by Northern-blot analysis. The polyphenols decreased DNA synthesis and cell viability in a dose-dependent manner. The increase in ODC activity caused by changing the medium was inhibited by adding tea polyphenols. The inhibition of the enzyme was dependent on the structure of tea polyphenols. (-)-epigallocatechin and (-)-epigallocatechin gallate were effective, but (+)-catechin, (-)- epicatechin and (-)-epicatechin gallate did not inhibit ODC induction, suggesting that pyrogallol-type catechins inhibit the enzymic activity of ODC whereas catechol-type catechins are less inhibitory. ODC was not inhibited by tea polyphenols when they were added to the culture medium 2h after a change to fresh medium. Incubating the cells for 4h with tea polyphenols then washing them out did not recover ODC activity. The ODC mRNA level in the cells treated with green tea extract was comparable to that in the control cells. These results confirm that green tea extract inhibits ODC induction dose-dependently in Ehrlich ascites tumor cells and that the inhibition of its induction was dependent on the structure of the tea polyphenols. We found that the tea polyphenols caused a martivity with no detectable effect on ODC mRNA levels in the cells, suggesting that tea polyphenols inhibit ODC induction at the post-transcriptional level.

Prevention of photocarcinogenesis by topical administration of pure epigallocatechin gallate isolated from green tea

Nutrition and Cancer (USA) , 1996, 26/3 (325-335)
Topical application of purified (-)-epigallocatechin-3-gallate (EGCG), a polyphenolic antioxidant isolated from green tea, inhibited photocarcinogenesis in BALB/cAnNHsd mice with no visible toxicity. Mice were treated with 0, 10, or 50 mg of EGCG in 200 microl of acetone three times weekly for three weeks before ultraviolet (UV) treatments began and throughout the experiment. UV radiation consisted of five 30-minute exposures per week to banks of six FS40 Westinghouse sunlamps for 25 weeks. In the photocarcinogenesis study, mice received a total dose of approximately 2.1 x 106 J/m2. Skin cancer incidence in UV-irradiated mice was 96% at 28 weeks after the first UV treatment; EGCG at 10 or 50 mg reduced this incidence to 62% and 39%, respectively. UV-induced immunosuppression, assessed by the inability of UVB-irradiated mice to reject a syngeneic antigenic tumor, was not influenced by topical EGCG. Oral administration of 0, 100, or 500 mg of pure EGCG per liter of drinking water (approximately 0, 0.56, or 2.8 mg/day, respectively) did not decrease UV-induced skin tumor incidence, rate of primary tumor growth, or inability to reject antigenic tumors. Thus induction of skin tumors by UV radiation was significantly reduced by topical, but not by oral, administration of purified EGCG through a mechanism distinct from inhibition of photoimmunosuppression.

Natural antimutagenic agents may prolong efficacy of human immunodeficiency virus drug therapy

Medical Hypotheses (United Kingdom) , 1997, 48/3 (215-220)
The long-term efficacy of new combination drug therapies for human immunodeficiency virus infection may be limited by the tendency of transfected human immunodeficiency virus to mutate to drug-resistant forms. This argues for the use of safe antimutagenic measures as adjuvants to such therapies. Certain nutrients and food factors notably selenium, green-tea polyphenols, and cruciferous phytochemicals - can suppress cancer initiation and mutagenesis in animal and cell culture models; epidemiological studies suggest that ambient variations in consumption of these food factors can have an important impact on human cancer rates. Low-fat diets may reduce deoxyribonucleic acid base damage in human leukocytates. Thus, ample but safe intakes of selenium, green-tea polyphenols, and cruciferous vegetables, in the context of a diet low in fat and assimilable iron, can be expected to prolong the efficacy of drug therapy in subjects infected with the human immunodeficiency virus. These measures can also be recommended for cancer prevention in the general population.

Prevention of photocarcinogenesis by topical administration of pure epigallocatechin gallate isolated from green tea

Nutrition and Cancer (USA) , 1996, 26/3 (325-335)
Topical application of purified (-)-epigallocatechin-3-gallate (EGCG), a polyphenolic antioxidant isolated from green tea, inhibited photocarcinogenesis in BALB/cAnNHsd mice with no visible toxicity. Mice were treated with 0, 10, or 50 mg of EGCG in 200 microl of acetone three times weekly for three weeks before ultraviolet (UV) treatments began and throughout the experiment. UV radiation consisted of five 30-minute exposures per week to banks of six FS40 Westinghouse sunlamps for 25 weeks. In the photocarcinogenesis study, mice received a total dose of approximately 2.1 x 106 J/m2. Skin cancer incidence in UV-irradiated mice was 96% at 28 weeks after the first UV treatment; EGCG at 10 or 50 mg reduced this incidence to 62% and 39%, respectively. UV-induced immunosuppression, assessed by the inability of UVB-irradiated mice to reject a syngeneic antigenic tumor, was not influenced by topical EGCG. Oral administration of 0, 100, or 500 mg of pure EGCG per liter of drinking water (approximately 0, 0.56, or 2.8 mg/day, respectively) did not decrease UV-induced skin tumor incidence, rate of primary tumor growth, or inability to reject antigenic tumors. Thus induction of skin tumors by UV radiation was significantly reduced by topical, but not by oral, administration of purified EGCG through a mechanism distinct from inhibition of photoimmunosuppression.

Chemopreventive effects of green and black tea on pulmonary and hepatic carcinogenesis

Fundamental and Applied Toxicology (USA) , 1996, 29/2 (244-250)
The chemopreventive effects of decaffinated green and black tea treatment on liver and lung tumorigenesis were examined in carcinogen-treated mice. Male C3H mice were given decaffeinated green or decaffeinated black tea in their drinking water prior to, during, and after treatment with diethylnitrosamine (50 microg/kg bw, ip, once per week for 8 weeks). After 40 weeks of tea treatment, mice were sampled and examined for pulmonary and hepatic tumors. Mice treated with both DENA and tea displayed a significant decrease in the mean number of lung and liver tumors compared to DENA-only treated animals. Mice that received 0.63 or 1.25% green tea or 1.25% black tea exhibited a reduction in liver tumor numbers of 54, 50, and 63%, respectively from that seen in the DENA-only treated mice. Tea treatment also significantly decreased the multiplicity of lung adenomas. Mice receiving DENA and either 0.63 or 1.25% green tea or 1.25% black tea showed a decrease in the mean number of lung tumors of 40, 46, and 34%, respectively, from DENA-only treated mice. While a possible association between the chemopreventive activity of tea on lung tumor response and the concentration of (-) epigallocatechin gallate (EGCG) in the tea was suggested, no apparent relationship between EGCG concentration and liver tumor response was seen, however. These results show a dose-dependent chemoprevention of both lung and liver tumors by both black and green tea in diethylnitrosamine-treated C3H mice.

Nutrition and esophageal cancer

Cancer Causes and Control (United Kingdom) , 1996, 7/1 (33-40)
Epidemiologic evidence on the relation between nutrition and esophageal cancer is reviewed. Results from ecologic, case-control, cohort, and intervention studies are included. Most of the findings pertain more to squamous cell carcinoma than adenocarcinoma of the esophagus. The protective effect of fruit and vegetable consumption is supported by a large body of evidence, especially from case-control studies. The effects of food groups and nutrients other than fruits and vegetables also have been examined, but the overall evidence is less convincing. Recent intervention studies in high incidence areas in China indicate that micronutrient supplements may have a modest effect in reducing risk, but the generalizability of this result is uncertain. Hot drinks are likely to increase the risk of esophageal cancer. On the other hand, the role of tea drinking, especially the use of green tea, remains to be defined better.