Detection and chemical identification of natural bio-antimutagens. A case of the green tea factor

Antimutagenicity of hydrolyzable tannins from Terminalia chebula in Salmonella typhimurium

A tannin fraction (TC-E) from the dried fruit pulp of Terminalia chebula was obtained by successfully extracting with 95% ethyl alcohol and ethyl acetate. TC-E was subjected to silica gel chromatography which yielded four fractions, viz., TC-EI, TC-EII, TC-EIII and TC-EIV. Thin layer chromatography (TLC) and 13C-NMR revealed that TC-EI was gallic acid (GA) derivative while the other fractions were tannin in nature. TC-E and its fractions were evaluated for their antimutagenic potential against two direct-acting mutagens, 4-nitro-o-phenylenediamine (NPD) and 4-nitroquinoline-N-oxide (4NQNO), and S9-dependent mutagen, 2-aminofluorene (2AF) in TA98 and TA100 strains of Salmonella typhimurium. The study revealed that the extract (TC-E) and its fractions were highly significant against S9-dependent mutagen, 2AF. The effect was found to be more or less corresponding with the nature of the fractions, as the monomeric TC-EI (a GA derivative) was least effective as compared to other fractions which were oligomeric, and the order of their effectiveness as per their IbD50 value being TC-EIV (8.9 micrograms)>TC-EIII (17.8 micrograms)>TC-EII (45 micrograms)>TC-EI (320 micrograms) in TA98; TC-EIV being 40 times more effective than TC-EI in inhibiting his+ revertants. A similar effect was noticed in TA100 too, where TC-EI was the least effective and TC-EII had the maximum effect. A similar result was noticed when the antimutagenicity of GA (a monomeric) was compared with tannic acid (TA, an oligomeric). However, chebula tannins were found to be partly effective against NPD but not at all effective against 4NQNO.

Selection of column and gradient elution system for the separation of catechins in green tea using high-performance liquid chromatography

A study of a variety of stationary phases and elution conditions for the liquid chromatographic (LC) determination of six biologically active green tea catechins has resulted in the development of two well-defined, reproducible systems for such analyses which overcome limitations of previously described methods. Comparison of six reversed-phase columns indicates that deactivated stationary phases, which utilize ultrapure silica and maximize coverage of the silica support, provide significantly improved separation and chromatographic efficiencies for catechin analyses using LC, compared to conventional monomeric or polymeric C18 columns. Evaluation of elution conditions used for the separations reveals that the presence of acid in the mobile phase (0.05% trifluoroacetic acid) is essential for both the complete resolution of the catechins present in tea and the efficient chromatography of these compounds. The efficacy of one of the developed systems was demonstrated by the quantitative measurement of the six biologically active catechins in aqueous infusions of green tea (Camellia sinensis). Overall precision values for the analyses were within the range 0.3-1% (relative standard deviation).

Potent suppressing activity of the non-polyphenolic fraction of green tea (Camellia sinensis) against genotoxin-induced umu C gene expression in Salmonella typhimurium (TA 1535/pSK 1002)--association with pheophytins a and b

Antigenotoxic and antimutagenic activities of green tea extract and tea-derived polyphenols have been studied using in vitro and in vivo experiments. However, antigenotoxic substances in the non-polyphenolic fraction of green tea have been poorly elucidated. In the present study, the effect of the non-polyphenolic fraction of green tea on genotoxin-induced umu C gene expression was analyzed using a tester bacteria, and potent antigenotoxic substances in the non-polyphenolic fraction were identified. The non-polyphenolic fraction of green tea showed strong suppressive activities against umu C gene expression in Salmonella typhimurium (TA 1535/pSK 1002) induced by 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indol (Trp-P-1) or mitomycin C (MMC) in the presence or absence of S9 metabolizing enzyme mixture. The non-polyphenolic fraction of green tea exhibited major two-color bands in a silica gel TLC and they were identified as chlorophyll-related compounds, pheophytins a and b, judged by their specific colors, Rf values in silica gel TLC and absorption spectra. These pigments showed significant suppressive activities against umu C gene expression in tester bacteria induced by Trp-P- and MMC in a dose-dependent manner. These results suggest that the non-polyphenolic fraction of green tea contains pheophytins a and b as potent antigenotoxic substances.

Possible mechanisms of antimutagens by various teas as judged by their effects on mutagenesis by 2-amino-3-methylimidazo[4,5-f]quinoline and benzo[a]pyrene

Possible mechanisms of antimutagenicity of various tea extracts (green, pouchong, oolong and black tea) toward 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and benzo[a]pyrene (B[a]P) were investigated using a Salmonella/microsome assay. Tea extracts exhibited no inhibitory effects toward IQ and B[a]P in bio-antimutagenic assays, indicating that their antimutagenic activity is desmutagenic in nature. The mutagenicities of IQ and B[a]P decreased as the reaction periods of tea extracts with promutagens, S9 mix, or mutagen metabolites increased. The antimutagenicity of tea extracts toward IQ could be attributed (primarily) to an interaction between tea extracts and S9 mix. Apart from their interaction with S9 mix, tea extracts also exhibited antimutagenicity by markedly decreasing the mutagenicity of B[a]P metabolites. These results suggest that tea extracts: (1) inhibit the cytochrome P-450-mediated metabolism of IQ and B[a]P to their ultimate mutagenic metabolite form; and (2) interact with both promutagens and their metabolites in such a way as to reduce their mutagenic potentials. Therefore, the antimutagenic actions of tea extracts are due to a combination of the above distinctive mechanisms, and can vary with the type of mutagen under test.

Antimutagenicity of Tochu tea (an aqueous extract of Eucommia ulmoides leaves): 1. The clastogen-suppressing effects of Tochu tea in CHO cells and mice

The suppressing effect of crude extracts of Tochu tea, an aqueous extract of Eucommia ulmoides leaves and a popular beverage in Japan, on the induction of chromosome aberrations in CHO cells and mice was studied. When CHO cells were treated with Tochu tea crude extract after MMC treatment, the frequency of chromosome aberrations was reduced. Out of 17 Tochu tea components, 5 irridoids (geniposidic acid, geniposide, asperulosidic acid, deacetyl asperulosidic acid, and asperuloside) and 3 phenols (pyrogallol, protocatechuic acid, and p-trans-coumaric acid) were found to have anticlastogenic activity. Since the anticlastogenic irridoids had an alpha-unsaturated carbonyl group, this structure was considered to play an important role in the anticlastogenicity. The anticlastogenic effect of Tochu tea extracts was examined in mice using a micronucleus assay. When mice received 1.0 ml 4% Tochu tea extract by oral gavage 6 h before intraperitoneal injection of MMC, a decrease in the frequency of micronuclei was observed. This decrease was not due to a delay in the maturation of micronucleated reticulocytes.

Green tea polyphenols inhibit oxidant-induced DNA strand breakage in cultured lung cells

The influence of green tea polyphenols (GTP) on the formation of DNA strand breaks (DNA-SB) and lipid peroxidation products (LPP) in cultured human lung cells (A 549) exposed to different oxidants was investigated. Cells were pretreated with GTP for 2 h and then exposed to cigarette smoke solution, H2O2 or FeCl3 for 30 min. After exposure, the cells were analyzed for DNA-SB, LPP, and viability. In addition, the effects of GTP added directly to the incubation mixtures during exposure were examined, using the same end points. It appeared that pretreatment with GTP inhibited both cigarette smoke- and H2O2-induced DNA breakage; i.e., following exposure to cigarette smoke or H2O2, the fraction of DNA passing through a microfilter increased significantly in cells not subjected to GTP, but this effect was prevented or inhibited in GTP-treated cells. Pretreatment with GTP also reduced the overall toxicity of H2O2 as determined by cell growth after exposure. Moreover, addition of GTP during exposure reduced both cigarette smoke- and H2O2-induced DNA breakage as well as formation of LPP after exposure to Fe3+. These results indicate that GTP inhibit the formation of DNA-SB in cells exposed to oxidants. It is possible that this ability to GTP to inhibit DNA-SB formation might contribute to the antitumorogenic properties of green tea.

Antimutagenicity of Tochu tea (an aqueous extract of Eucommia ulmoides leaves): 2. Suppressing effect of Tochu tea on the urine mutagenicity after ingestion of raw fish and cooked beef

The effect of Tochu tea, which is an aqueous extract of Eucommia ulmoides leaves and a popular-beverage in Japan, on the urine mutagenicity before and after ingestion of raw fish and cooked beef was studied using Salmonella typhimurium YG1024. Urines were collected from seven healthy, non-smoking Japanese women before and after ingestion of raw fish and cooked beef. In experiment 1,3 were in a control group and 4 were in a Tochu tea-drinking group (2000 ml per day). The mutagenicity of urine from the Tochu tea-drinking group was much lower. In experiment 2 the 7 women switched groups; the tea-drinking group became the control group, and the control group became the Tochu tea-drinking group. Again, the mutagenicity of urine collected from the Tochu tea-drinking group was much lower. These results suggest that the decrease in the mutagenicity of the urine from the Tochu tea-drinking group was due to the intake of Tochu tea, but not to individual differences. Thus, the ingestion of Tochu tea may reduce human exposure to dietary mutagens.

Bio-antimutagenic activity of green tea catechins in cultured Chinese hamster V79 cells

The antimutagenic effects of green tea catechins, (-)-epicatechin gallate (ECg) and (-)-epigallocatechin gallate (EGCg) on induction of 6-thioguanine (6TG)-resistant mutations induced by 4-nitroquinolin 1-oxide (4NQO) were found in cultured Chinese hamster V79 cells. The antimutagenic activity of catechins was found only when cells were post-treated with catechins during the mutation expression time after treatment with 4NQO, and not found by simultaneous treatments with 4NQO and catechins. This bioantimutagenic activity of catechins were not observed in ethyl methanesulfonate (EMS)-induced mutations. This suggests that the antimutagenic effects of catechins may act intracellularly as bio-antimutagenic blocking agent or suppressive agent. These catechins had no effects on the cytotoxic activity of 4NQO in V79 cells, whether catechins were used in simultaneous treatment with or in post-treatment after 4NQO. This indicates that the antimutagenicity and anticytotoxicity to 4NQO may be caused by different mechanism(s).

Bacterial mutagenicity of terasi and antimutagenicity of Indonesian jasmine tea against terasi

Terasi, a traditional fermented product of Indonesia was evaluated by Salmonella mutagenesis assay. The higher the heating temperature and the longer the heating time, the more mutagenicity observed in both terasi and its starter, and the highest mutagenic activity was shown by heating each of them at 100 degrees C for 60 min. Terasi starter has stronger mutagenic properties as compared to terasi. Indonesian jasmine tea, which is a yellow tea, was examined for its antimutagenic properties against mutagenic terasi. Tea component presented in fraction C (water soluble, chloroform and ethyl acetate insoluble fraction) as well as in fraction D (water soluble, chloroform, ethyl acetate and n-butanol insoluble fraction) were found to suppress the mutagenicities exerted by heated terasi and heated terasi starter. Yet, the tea components presented in fraction E (chloroform soluble fraction) were found to enhance the mutagenicity of terasi.

Palmitic acid is the major fatty acid responsible for significant anti-N-methyl-N'-nitro-N-nitroguanidine (MNNG) activity in yogurt

We describe here the isolation and identification of palmitic acid as being responsible for significant anti-N-methyl-N'-nitro-N-nitroguanidine (MNNG) activity in yogurt. The Ames test (Salmonella typhimurium TA100) was used to direct fractionation of activity. Yogurt was freeze-dried and extracted with acetone to yield a crude extract. The crude extract was purified by normal phase silica gel, Sephadex LH-20, and reversed phase medium pressure liquid chromatographies. The major compound in the active medium pressure liquid chromatographic fractions was determined to be palmitic acid on GC and high pressure liquid chromatography (HPLC) systems, and by nuclear magnetic resonance (NMR) analysis. Other saturated straight chain and methyl branched fatty acids were detected by GC/MS and were later shown to possess anti-MNNG activity. Of the straight chain fatty acids, palmitic acid had the highest anti-MNNG activity. All omega - 1 methyl branched fatty acids tested were more active than their straight chain counterparts. A trace amount of isopalmitic acid (14-methyl pentadecanoic acid), a minor milk lipid, was detected in one of the active fractions, and was later shown to be five times more active than palmitic acid. Isopalmitic acid also inhibited mutagenesis induced 4-nitroquinoline-N-oxide (4NQO), and 7, 12-dimethyl benz[a]anthracene (DMBA), and was found to inhibit the metabolic activation of DMBA.

Epigallocatechin gallate. The major causative agent of green tea-induced asthma

We describe three patients who worked in green tea factories and developed asthmatic and nasal symptoms after exposure to green tea dust. To clarify what component(s) of green tea leaves might be responsible for causing asthma, we prepared catechins, the major components of green tea leaves. Epigallocatechin gallate (EGCg; MW: 458 daltons), a major catechin, was purified by high-performance liquid chromatography. Subjects included three patients with green tea-induced asthma, five asthmatics with no previous exposure to tea dust, and five healthy controls. It was found that all three patients exhibited an immediate skin and bronchial response to EGCg. Prausnitz-Küstner test with EGCg was also positive. However, none of the asthmatic and healthy controls showed a positive reaction. These results indicate that EGCg is a causative agent of green tea-induced asthma and suggest that an IgE-mediated response is, at least in part, responsible for causing this type of occupational asthma.

Role of chemopreventers in human diet

Recent research has confirmed that many common foods contain nonnutritive components that may provide protection against chronic disease including some forms of cancer. These naturally occurring compounds, which possess anticarcinogenic and other beneficial properties, are referred to as chemopreventers. The predominant mechanism of their protective action is due to their antioxidant activity and the capacity to scavenge free radicals. Among the most investigated chemopreventers are some vitamins, plant polyphenols, flavonoids, catechins, and some components in spices. The majority of chemopreventers are available in and consumed from vegetables, fruits, grains, and tea. Various naturally occurring chemicals in garlic, soybeans, tea, and red wine appear to be responsible for the beneficial effect of these commodities on several chronic diseases. This article will review some recent studies in the search for the beneficial effects of dietary chemopreventers on human health.

Green tea and skin--anticarcinogenic effects

Because of its special aroma, green tea is a popular beverage consumed by some human populations worldwide. In recent years, many laboratory studies have shown that in a variety of animal tumor bioassay systems the administration of green tea, specifically the polyphenolic fraction isolated from green tea leaves (green tea polyphenols), affords protection against cancer induction. In mouse skin tumor bioassay systems, topical application of green tea polyphenols to skin has been shown to result in protection against a) 3-methylcholanthrene-induced skin tumorigenicity, b) 7,12-dimethylbenz(a)anthracene (DMBA)-induced skin tumor initiation, c) 12-O-tetradecanoylphorbol-13-acetate and other tumor promoters caused tumor promotion in DMBA-initiated skin, and d) benzoyl peroxide- and 4-nitroquinoline N-oxide caused enhanced malignant progression of nonmalignant lesions. Green tea extract has also been shown to cause partial regression of established skin papillomas in mouse. Similarly, chronic oral feeding of green tea polyphenols or water extract of green tea has also been shown to result in the protection against both chemical carcinogen- and ultraviolet B radiation-induced skin tumorigenicity. Collectively these data suggest that green tea possesses significant chemopreventive effect against each stage of carcinogenesis, and that it may be useful against inflammatory responses associated with the exposure of skin to chemical tumor promoters as well as to solar radiation. Available data regarding the mechanism by which green tea affords these diversified effects is discussed.

Antitransforming activity of chlorophyllin against selected carcinogens and complex mixtures

Chlorophyllin, a derivative of chlorophyll, is known to be an antimutagenic agent. Studies were performed to determine whether chlorophyllin can also inhibit morphological transformation of BALB/3T3 cells induced by carcinogens and complex mixtures. Chlorophyllin was added to the cultures simultaneously with carcinogens or complex mixtures while the transformation assay was conducted. At concentrations that did not significantly affect cell growth, chlorophyllin was found to inhibit morphological transformation induced by N-methyl-N'-nitro-N-nitrosoguanidine, 3-methylcholanthrene, 7,12-dimethylbenz(a)anthracene, benzo(a)pyrene, aflatoxin B1, and extracts of coal dust, tobacco snuff, and chewing tobacco. In all cases, the mean number of transformed foci per flask treated with chlorophyllin was significantly lower than that of untreated cultures. The reduction in the number of transformed foci was dependent on the concentration of chlorophyllin tested. These results indicate that chlorophyllin is an antitransforming agent.

A very low dose of green tea polyphenols in drinking water prevents N-methyl-N-nitrosourea-induced colon carcinogenesis in F344 rats

The effect of tea polyphenols, major constituents of tea, on colon carcinogenesis was investigated. A total of 129 female F344 rats were given an intrarectal instillation of 2 mg of N-methyl-N-nitrosourea 3 times a week for 2 weeks, and received a water solution of green tea extract (GTE) as drinking water throughout the experiment. Autopsies at week 35 revealed significantly lower incidence of colon carcinomas in rats ingesting 0.05%, 0.01% or 0.002% GTE solution than in controls ingesting 0% GTE solution: 43%, 40% and 33% vs. 67%. The data suggest that GTE, even at a very low dose (0.002% solution), has a potent inhibitory effect on colon carcinogenesis.

Inhibition of tobacco-specific nitrosamine-induced lung tumorigenesis by compounds derived from cruciferous vegetables and green tea

We have shown that PEITC and I3C, both of cruciferous origin, inhibited lung tumor formation induced by the tobacco-specific nitrosamine NNK. The inhibition by PEITC is due largely to its inhibitory effect on the enzymes of NNK metabolism, whereas; the inhibition by I3C may be attributed to its ability to induce hepatic enzyme activity of NNK metabolism, which resulted in decreased availability of NNK to the lung. On a molar basis, PEITC is considerably more effective than I3C. PEITC was released upon consumption of watercress. The N-acetylcysteine conjugate of PEITC is a promising urinary marker for quantitating uptake of this dietary anticarcinogen in humans. These studies also showed that green tea polyphenol EGCG inhibited the NNK-induced lung tumorigenesis, probably due to its antioxidant property. These studies provide for the first time evidence for the involvement of free radicals in nitrosamine tumorigenesis. The mechanism by which free radicals are generated by NNK treatment is not yet known. The reduced levels of oxidative lesions in lung as a result of EGCG treatment may be related to its ability to reduce reactive oxygen species and/or to chelate iron ion resulting in a decreased production of hydroxyl radicals. Overall, these studies have identified ingredients in cruciferous vegetables and green tea that are inhibitory against lung tumorigenesis induced by NNK in rodents.

The clastogen-suppressing effects of green tea, Po-lei tea and Rooibos tea in CHO cells and mice

The suppressing effects of crude extracts of three kinds of tea-green tea (GT) from Japan, Po-lei tea (PT) from China, and Rooibos tea (RT) from South Africa-on the induction of chromosome aberrations in cultured CHO cells and mice were studied. When CHO cells were exposed to each tea extract in the presence of rat liver microsomal enzymes (S9 mix) together with benzo[a]pyrene (B(a)P) or mitomycin C (MMC), a decrease in the frequency of chromosome aberrations was observed. PT and RT, but not GT, also suppressed the induction of chromosome aberrations by MMC in the absence of S9 mix. When cells were treated with tea extract after B(a)P or MMC treatment, RT suppressed the induction of chromosome aberrations in the presence and absence of S9 mix whereas GT and PT showed suppressing effects only in the presence of S9 mix. These data suggest that catechines, well-known antimutagens in tea samples, might account for the inhibitory effect in the case of GT and PT. Since RT contains few catechines, several unknown antimutagenic components could be responsible for its effect. The antimutagenic effects of tea extracts at concentration levels consumed by humans were examined in mice using micronucleus induction with B(a)P or MMC. When mice received oral gavage of 0.2% GT, 0.1% PT, and 0.1% RT at 1.0 ml/mouse 6 h before intraperitoneal injection of MMC, a decrease in the frequency of micronuclei was observed. The induction of micronuclei by B(a)P was suppressed by oral dosage of GT, PT and RT at 1.0 ml/mouse/day for 28 days. This was not due to a delay in the maturation of micronucleated reticulocytes. In conclusion, intake of tea might suppress the mutagenic activity of certain potent mutagens in human beings.

Inhibitory effects of tea extracts and (-)-epigallocatechin gallate on DNA synthesis and proliferation of hepatoma and erythroleukemia cells

Polyphenols extracted from green or black tea with ethyl acetate were strongly inhibitory for DNA synthesis in HTC rat hepatoma cells and DS19 mouse erythroleukemia cells at concentrations of 0.1-0.2 mg/ml. There was less inhibition with a subsequent black tea fraction extracted with butanol and with the residual water-soluble fraction. Although cell proliferation was inhibited by (-)-epigallocatechin gallate and the tea extracts, there were only marginal effects on differentiation of DS19 cells as judged by hemoglobin synthesis.

Identification of natural antimutagens with modulating effects on DNA repair

The results of a study of bioantimutagenesis, with emphasis on natural antimutagens from plant extracts with modulating effects on DNA repair in Escherichia coli bacteria are presented in this chapter. Comparative screening for spontaneous or induced mutagenesis, as well as expression of the SOS gene, sfiA was accomplished. Antimutagenic capacity was obtained with nontoxic concentrations of the plant extracts; the same plant extract may decrease or increase the mutation rate, or even be ineffective, depending on the bacterial strain used and the concentration of the extract applied. Since antimutagenic effects may be the consequence of either stimulation of error-free repair, inhibition of error-prone repair, or involvement of multiple mechanisms, the effects of several plant extracts on the level of UV-induced beta-galactosidase were screened (to monitor SOS induction in cells). Reduction of the enzyme activity induced by UV was observed following addition of St. John's wort extract, while there was not reduction after thyme, aloe, camomile, or lime-tree and the level of UV-induced enzyme was even higher with sage extract. Our results indicate that the antimutagenic effect of St. John's wort is probably due to suppression of error-prone repair. Moreover, we assume that an antimutagenic effect obtained with thyme, mint, and sage under certain conditions may be due to enhanced error-free repair.

Tea catechins decrease micellar solubility and intestinal absorption of cholesterol in rats

A(-)-epicatechin (EC) and (-)-epigallocatechin (EGC) mixture and a mixture of their gallates (ECG and EGCG, respectively) markedly lowered lymphatic cholesterol absorption in rats with a cannulated thoracic duct. A mixture of ECG and EGCG was more effective in reducing cholesterol absorption than the EC and EGC mixture. These catechins also tended to decrease lymphatic absorption of triacylglycerols, although not so pronounced as in cholesterol absorption. An in vitro study on micellar solubility of cholesterol showed that these catechin mixtures precipitated cholesterol solubilized in mixed bile salt micelles in a dose-dependent manner. A mixture of ECG and EGCG more effectively precipitated micellar cholesterol than a mixture of EC and EGC. When purified EC, EGC, ECG and EGCG were used, EGCG was more effective in precipitating micellar cholesterol than ECG. The effect of EC and EGC was comparable and weaker than their gallate esters. The bile acid concentration in the micelles was not affected by these catechins. A positive correlation was observed between the amount of coprecipitated EGCG and cholesterol. These results clearly show that tea catechins, in particular their gallate esters, effectively reduce cholesterol absorption from the intestine by reducing solubility of cholesterol in mixed micelles. The observation accounts for the hypocholesterolemic effect of tea catechins.

Tea components: antimutagenic and anticarcinogenic effects

BACKGROUND

Tea from the Camellia sinensis species of the Theaceae family is one of the most ancient and, next to water, the most widely consumed beverage in the world. Since tea contains several polyphenols and since several other naturally occurring dietary polyphenols have shown antimutagenic effects in bacteria and anticarcinogenic effects in animal bioassay systems, we studied whether polyphenols extracted from Chinese green tea (GTP) also possess antimutagenic and anticarcinogenic effects.

RESULTS

GTP and its constituent epicatechin derivatives were found to interact with hepatic cytochrome P450 (P450) and inhibited the P450-dependent mixed-function oxidase enzymes in skin and liver. GTP and its epicatechin derivatives exhibited antimutagenic effects in several test systems. GTP showed substantial anti-skin-tumor-initiating and anti-skin-tumor-promoting activities when assessed in murine skin tumorigenesis bioassay systems. In these model systems polyaromatic hydrocarbons, benzo[a]pyrene (BP), 3-methyl-cholanthrene, 7,12-dimethylbenz[a]anthracene, and (+)-7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9,10- tetrahydrobenzo[a]pyrene (an ultimate carcinogenic metabolite of BP) were used as model skin carcinogens. The feeding of GTP in drinking water to SKH-1 hairless mice also afforded significant protection against ultraviolet-B-radiation-induced skin photocarcinogenesis.

CONCLUSIONS

These data suggest that tea components possess antimutagenic and anticarcinogenic effects, and that they could protect humans against the risk of cancer by environmental agents.

Combined mutagenicity of methyl methanesulfonate and ethyl methanesulfonate in Chinese hamster V79 cells

The combined effects of methyl methanesulfonate (MMS) and ethyl methanesulfonate (EMS) on the induction of 6-thioguanine (6TG)-resistant mutants and chromosome aberrations were examined in Chinese hamster V79 cells. Cells were simultaneously treated with EMS at a concentration of D20 and MMS at various concentrations for 3, 6 or 9 h. In other experiments cells were simultaneously treated with MMS at a concentration of D20 and EMS at various concentrations for 3, 6 or 9 h. The mathematical analysis of the combined effects of both chemicals for cell killing (cytotoxicity) and 6TG-resistant mutations indicates that synergistic interactions were observed for both cell killing and mutations induced by MMS and EMS. The frequency of chromosome aberrations induced by simultaneous treatment with MMS at a concentration of D20 and EMS at various concentrations for 3 h was additive. However, the frequency of chromosome aberrations induced by EMS at a concentration of D20 and MMS at various concentrations for 3 h was not significantly different from those induced by MMS alone.

(-)-Epigallocatechin-3-gallate in Camellia sinensis leaves from Himalayan region of Sikkim: inhibitory effects against biochemical events and tumor initiation in Sencar mouse skin

Recently, we and others showed that the components of green tea may be useful cancer chemopreventive agents. It has been suggested that (-)-epigallocatechin-3-gallate (EGCG), the major constituent in green tea, may possess antitumor-promoting and/or anticarcinogenic effects in rodent tumor bioassay systems. During the chemical analysis of various green tea products, we found a traditionally preserved preparation of green tea used by tribes in the Himalayan region of Sikkim, India that was rich in EGCG. EGCG was isolated from this tea product, and its inhibitory effects were evaluated against the binding of topically applied 3H-labeled polycyclic aromatic hydrocarbons (PAHs) to epidermal DNA and 12-O-tetradecanoylphorbol-13-acetate (TPA) caused induction of epidermal ornithine decarboxylase (ODC) activity in Sencar mice, the short-term markers of tumor initiation and tumor promotion, respectively. Preapplication of EGCG resulted in significant inhibition (p less than 0.05) in the binding of [3H]PAH to epidermal DNA. Similarly, the topical application of EGCG resulted in significant inhibition (p less than 0.005) in TPA-caused induction of epidermal ODC activity. In further studies, we assessed the anti-skin tumor-initiating effect of EGCG in Sencar mice in an initiation-promotion protocol. The application of EGCG before challenge with 7,12-dimethylbenz[a]anthracene as tumor initiator resulted in significant reduction both in percentage of mice with tumors and number of tumors per mouse compared with a non-EGCG-pretreated group of animals. The results of the present study suggest that the green tea preparation from Sikkim may be a good source for the isolation of EGCG and that this compound may have significant potential as a cancer chemopreventive agent.

Radioprotective effects of (-)-epigallocatechin 3-O-gallate (green-tea tannin) in mice

Long-term administration of (-)-epigallocatechin 3-O-gallate (EGCG) to mice through drinking water prevented radiation-induced increase of lipid peroxides in liver and significantly prolonged life span after lethal whole-body X-irradiation. The result indicates validity of this green-tea component as an orally active radio-protector of very low toxicity.

Antimutagenic effects of mushrooms

A heat-resistant factor in ethanol extracts of the fungus Craterellus cornucopioides completely inhibited the mutagenicity of aflatoxin B1, benzo[a]pyrene, the acridine half mustard ICR-191 and 2-nitrofluorene in a forward-mutation system using Salmonella typhimurium TM677 (screening for 8-azaguanine resistance). There was no inhibitory effect on the mutagenic activity of 4-nitroquinoline-N-oxide, methyl methanesulfonate or N-methyl-N'-nitro-N-nitrosoguanidine. Experiments performed to elucidate the mechanism of the antimutagenic effect showed that neither an alteration of cell viability nor an interference with the excision-repair and the inducible SOS-repair system was involved. The conceivable mechanisms for the antimutagenicity of the ethanol extract include direct chemical interaction with the mutagen and/or inhibition of the activation process in the case of the promutagens. The antimutagenic activity of Craterellus cornucopioides is not unique among mushroom species. The ethanol extracts of 6 other mushrooms showed a similar antimutagenic activity.

In vivo anticlastogenic and antimutagenic effects of tannic acid in mice

The anticlastogenic effect of tannic acid was studied in vivo in the mouse micronucleus test. The frequencies of micronuclei induced by mitomycin C, ethyl nitrosourea (ENU) or 4-nitroquinoline 1-oxide in mouse bone marrow cells were decreased by the oral administration of tannic acid 6 h before the mutagen injection. The observed suppressing effect was not a reflection of a delay in the formation of micronuclei by the cytotoxic effect of tannic acid. The antimutagenic effect of tannic acid was also investigated in vivo in the mouse spot test using male PW and female C57BL/10 mice. Tannic acid was given orally to pregnant females 6 h before the intraperitoneal injection of ENU on the 10th day of pregnancy. The frequency of pups with recessive color spots induced by ENU was decreased by the administration of tannic acid. The observed decrease was not due to toxic effects on the embryo. These results indicate that tannic acid acts as an anticlastogen and antimutagen in vivo.

Antimutagenic activity of green tea polyphenols

For centuries green tea has been a widely consumed beverage throughout the world. It is known to contain a number of pharmacologically active compounds. In this study water extracts of green tea (WEGT) and their major constituents, green tea polyphenols (GTP), were examined for antimutagenic activity. WEGT and GTP were found to significantly inhibit the reverse mutation induced by benzo[alpha]pyrene (BP), aflatoxin B1 (AFB1), 2-aminofluorene, and methanol extracts of coal tar pitch in Salmonella typhimurium TA100 and/or TA98 in the presence of a rat-liver microsomal activation system. GTP also inhibited gene forward mutation in V79 cells treated with AFB1 and BP, and also decreased the frequency of sister-chromatid exchanges and chromosomal aberrations in V79 cells treated with AFB1. The addition of GTP during and after nitrosation of methylurea resulted in a dose-dependent inhibition of mutagenicity. Studies to define the mechanism of the antimutagenic activity of GTP suggest that it may affect carcinogen metabolism, DNA adduct formation, the interaction of ultimate carcinogen or the scavenging of free radicals.

Crude tea extracts decrease the mutagenic activity of N-methyl-N'-nitro-N-nitrosoguanidine in vitro and in intragastric tract of rats

The effects of tea extracts and their ingredients, catechins and L-ascorbic acid (AsA), on the mutagenicity of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) were examined in vitro and in the stomachs of rats using E. coli WP2 and S. typhimurium TA100. The extracts of green tea and black tea leaves decreased the mutagenic activity of MNNG to E. coli WP2 in vitro in a desmutagenic manner. Catechins such as (-)-epigallocatechin from green tea leaves and the low-molecular-weight tannin fraction isolated from black tea extract with HP-20 resin also exhibited inhibitory effects against the mutagenic activity of MNNG. A desmutagenic effect of AsA on MNNG-induced mutagenicity was observed depending on the dose, though it was complicated. The effects were also demonstrated in the stomachs of rats by assaying the bacterial mutagenic in vitro; the tea extracts previously given orally to rats reduced the mutagenic activity of MNNG remarkably, though simultaneous administration showed less effect. The effectiveness of tea extracts for the decrease of MNNG-induced mutagenesis in vitro and in vivo suggests that the habitual drinking of tea may reduce the tumor-initiating potency of MNNG-type nitrosoureido compounds if they are formed in the stomach.

Antimutagenesis by factors affecting DNA repair in bacteria

The term 'antimutagen' was originally used to describe an agent that reduces the apparent yield of spontaneous and/or induced mutations, regardless of the mechanisms involved. The 'antimutagens' include 'desmutagens' and 'bio-antimutagens'. In this article, our attention was focused on the bio-antimutagens affecting DNA repair in bacteria. Cobaltous chloride reduced the frequency of mutations in Escherichia coli induced by MNNG. The possibility that metal compound inhibits the growth of mutagen-treated cells was examined. The results clearly showed that the antimutagen surely reduces the mutation rate. The target of cobaltous chloride was found to be cellular factors including Rec A. Vanillin and cinnamaldehyde had strong antimutagenic activities against UV, 4NQO and AF-2. They stimulated Rec A-dependent recombination repair functions in the mutagen-treated cells. Among plant materials, tannins possess antimutagenic activity against UV-induced mutations in E. coli. It has been found that tannic acid stimulates the excision repair encoded by the uvrA gene thereby reducing the yield of mutants. Substances which are antimutagenic in bacterial systems also had antimutagenic activity in cultured mammalian cell systems. Vanillin reduced the frequency of mutagen-induced chromosomal aberrations.