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.     

A potent thromboxane formation inhibitor in green tea leaves

A ninhydrin positive compound (L2) now identified as 2-amino-5-(N-ethylcarboxyamido)-pentanoic acid, from unprocessed tea leaves was a potent inhibitor of thrombin-stimulated thromboxane formation in rabbit whole blood (Ali and Afzal; Prostaglandins, Leukotrienes and Medicine, 27: 9, 1987). In the present study, processed and unprocessed tea leaf extracts were given to rats to consume for a period of eight weeks. Cholesterol and thromboxane levels were measured in the serum obtained from clotting the blood at 37 degrees C. A significant reduction in thromboxane levels was observed in rats taking unprocessed tea extract. This reduction was equally distributed in adult as well as in juvenile rats. However no appreciable changes in the levels of thromboxane were noticed in the serum of rats taking processed tea extracts. This might be due to the presence of a labile component which is destroyed during the processing of green tea leaves. A decreased level of cholesterol was observed in rats consuming unprocessed tea extract. This decrease could be linked to the decrease in thromboxane levels as observed. Processed tea refers to commercially available tea of different brands while unprocessed tea refers to dried green tea leaves.     

Scavenging of hydrogen peroxide and inhibition of ultraviolet light-induced oxidative DNA damage by aqueous extracts from green and black teas

Aqueous extracts of green and black teas have been shown to inhibit a variety of experimentally induced animal tumors, particularly ultraviolet (UV) B light-induced skin carcinogenesis. In the present study, we compared the effects of different extractable fractions of green and black teas on scavenging hydrogen peroxide (H2O2), and UV irradiation-induced formation of 8-hydroxy 2'-deoxyguanosine (8-OHdG) in vitro. Green and black teas have been extracted by serial chloroform, ethyl acetate and n-butanol, and divided into four subfractions designated as GT1-4 for green tea and BT1-4 for black tea, respectively. The total extracts from green and black teas exhibited a potent scavenging capacity of exogenous H2O2 in a dose-dependent manner. It appeared that the total extracts from black tea scavenged H2O2 more potently than those from green tea. When tested individually, the potency of scavenging H2O2 by green tea subfractions was: GT2 > GT3 > GT1 > GT4, whereas the order of efficacy for black tea was: BT2 > BT3 > BT4 > BT1. In addition, we demonstrated that total fractions of green and black teas substantially inhibited the induction of 8-OHdG in calf thymus by all three portions of UV spectrum (UVA, B and C). Consistent with the capacity of scavenging H2O2, the subfractions from black tea showed a greater inhibition of UV-induced 8-OHdG than those from green tea. At low concentrations, the order of potency of quenching of 8-OHdG by green tea subfractions was: GT2 > GT3 > GT4 > GT1 and the efficacy of all subfractions became similar at high concentrations. All subfractions of the black tea except BT1 strongly inhibited UV-induced 8-OHdG and the order of potency was: BT2 > BT3 > BT4 > BT1. Addition of (-)-epigallocatechin gallate (EGCG), an ingredient of green tea extract, to low concentration of green and black tea extracts substantially enhanced the scavenging of H2O2 and quenching of 8-OHdG, suggesting the important role of EGCG in the antioxidant activities of tea extracts. The potent scavenging of oxygen species and blocking of UV-induced oxidative DNA damage may, at least in part, explain the mechanism(s) by which green/black teas inhibit photocarcinogenesis.     

Different types of tea products attenuate inflammation induced in Trypanosoma brucei infected mice

An in vivo study was carried out to determine the effect of different types of Kenyan tea extracts on male Swiss albino mice infected with Trypanosoma brucei brucei isolate KETRI 2710. The isolate produced a similar clinical picture after a pre-patent period of 5 days post-infection (DPI). Parasitemia levels in the untreated mice and those given different teas developed exponentially at similar rates reaching similar densities at the peak of parasitemia 8 DPI. Between 9 and 13 DPI parasitemia decreased more rapidly in tea treated compared to the untreated mice which indicated that tea lowered parasitemia level. Anaemia indicated by a fall in erythrocyte packed cell volume (PCV) occurred within 4 DPI and remained below the normal levels until the terminal stages of the disease. A significant difference (P<0.05) was observed 11 DPI between the tea treated and the untreated mice indicating that tea enhanced resistance to erythrocyte destruction. Mice treated with tea exhibited significantly (P<0.01) reduced parasite-induced hypoalbuminemia as compared to the untreated. Since albumin is a negative acute phase protein, it shows a decrease during inflammatory conditions and therefore its elevation in the mice given tea in this study clearly demonstrated that tea ameliorated inflammation induced by T. b. brucei. Although green and white teas were superior in most of these characteristics, black tea, which is the principle tea product from Kenya, displayed remarkable properties some even comparable to those of green tea. Interestingly, tea was more efficacious than dexamethasone an established anti-inflammatory drug, demonstrating its therapeutic potential.     

Anti-mite activities of Clerodendrum viscosum Ventenat (Verbenaceae) extracts on tea red spider mite,Oligonychus coffeae Nietner (Acarina: Tetranychidae)

Acaricidal and ovicidal activities of Clerodendrum viscosum Ventenat (Verbenaceae), a common weed of India, were investigated on tea red spider mite, Oligonychus coffeae Nietner (Acarina: Tetranychidae). Different solvent extracts (water, methanol, acetone and petroleum ether) of C. viscosum at different concentrations (1, 2, 4 and 8%) were used. These solvent extracts exhibited mortality of O. coffeae in the range of 40–90% in water, 67–97% in petroleum ether, 50–80% in acetone and 43–87% in methanol extract. Depending on LC₅₀ values, the relative toxicity was found to be significantly highest against petroleum ether extracts and lowest in water extracts. Acetone extract of C.viscosum recorded maximum ovicidal activity followed by petroleum ether, methanol and the less by water extracts. In the field trials, mite population were significantly lower (P < 0.05) on plots sprayed with different of C. viscosum extracts than the control and at par with chemical acaricide and neem biopesticide. No phytotoxic effect (score, 0–5% and grade 1) was observed in the field from tea bushes sprayed with different doses of extracts of C. viscosum. Made tea samples were taint free. Organoleptic test revealed leaf infusions and liquor strength as good, scoring 6.5–7.0 on a 10-point scale. Availability and distribution of this weed (C. viscosum) in and around tea growing areas of sub-Himalayan region, along with its processing for the feasibility of including C.visosum extracts in the current IPM programme are discussed.     

Tea crude extracts effectively inactivate severe acute respiratory syndrome coronavirus 2

It is well known that black and green tea extracts, particularly polyphenols, have antimicrobial activity against various pathogenic microbes including viruses. However, there is limited data on the antiviral activity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which emerged rapidly in China in late 2019 and which has been responsible for coronavirus disease 2019 (COVID-19) pandemic globally. In this study, 20 compounds and three extracts were obtained from black and green tea and found that three tea extracts showed significant antiviral activity against SARS-CoV-2, whereby the viral titre decreased about 5 logs TCID₅₀ per ml by 1·375 mg ml⁻¹ black tea extract and two-fold diluted tea bag infusion obtained from black tea when incubated at 25°C for 10 s. However, when concentrations of black and green tea extracts were equally adjusted to 344 µg ml⁻¹, green tea extracts showed more antiviral activity against SARS-CoV-2. This simple and highly respected beverage may be a cheap and widely acceptable means to reduce SARS-CoV-2 viral burden in the mouth and upper gastrointestinal and respiratory tracts in developed as well as developing countries.     

Antimutagenic Activity of Water Extracts of Black Tea and Oolong Tea

Water extracts of leaves of black tea, oolong tea, and green tea, were examined for antimutagenic activity with Salmonella typhimurium test strains, TA 98 and TA 100. These water extracts significantly decreased the reverse mutation induced by crude dimethyl sulfoxide extracts of grilled beef and, by Trp-P-1, Glu-P-1, and B[a]P in the presence of a rat liver microsomal activation system. They also decreased the mutagenicity of AF-2 and 4-NQO requiring no metabolic activation to cause the mutation. Removal of caffeine from tea extracts did not influence the DEGB-induced mutation, but ethyl acetate extraction abolished the effect.     

Tea contains potent inhibitors of tyrosine phosphatase PTP1B

Tea is widely consumed all over the world. Studies have demonstrated the role of tea in prevention and treatment of various chronic diseases including diabetes and obesity, but the underlying mechanism is unclear. PTP1B is a widely expressed tyrosine phosphatase which has been defined as a target for therapeutic drug development to treat diabetes and obesity. In screening for inhibitors of PTP1B, we found that aqueous extracts of teas exhibited potent PTP1B inhibitory effects with an IC50 value of 0.4–4 g dry tea leaves per liter of water. Black tea shows the strongest inhibition activities, followed by oolong and then by green tea. Biochemical fractionations demonstrated that the major effective components in tea corresponded to oxidized polyphenolic compounds. This was further verified by the fact that tea catechins became potent inhibitors of PTP1B upon oxidation catalyzed by tyrosinases. When applied to cultured cells, tea extracts induced tyrosine phosphorylation of cellular proteins. Our study suggests that some beneficial effects of tea may be attributed to the inhibition of PTP1B.     

Green, oolong and black tea extracts modulate lipid metabolism in hyperlipidemia rats fed high-sucrose diet

The main goal of this study was to compare effects of ethanol-soluble fractions prepared from various types of teas on sucrose-induced hyperlipidemia in 5-week old male Sprague-Dawley rats. Rats (n = 6-8 per group) weighed approximately 200 g were randomly divided into control diet, sucrose-rich diet, green tea, oolong tea and black tea groups. Control-diet group was provided with modified AIN-93 diet while the others consumed sucrose-rich diet. Tea extracts (1% w/v) were supplied in the drink for green tea, oolong tea and black tea groups. Results indicated sucrose-rich diet induced hypertriglyceridemia and hypercholesterolemia. Food intake was reduced by oolong tea extract. Consuming oolong and black tea extracts also significantly decreased body weight gains and food efficiency. Hypertriglyceridemia was normalized by green and black tea drink on day 18 and by oolong tea extract on day 25, respectively. Hypercholesterolemia was normalized by green tea on day 18 and by oolong tea and black tea on day 25, respectively. Plasma HDL-cholesterol concentrations were not affected by any tea extract. The triglyeride content in the liver as well as the cholesterol content in the heart of rats fed sucrose-rich diet were elevated and were normalized by all types of tea drink tested. Although green and oolong tea extracts contained similar composition of catechin, our findings suggest green tea exerted greater antihyperlipidemic effect than oolong tea. Apparent fat absorption may be one of the mechanisms by which green tea reduced hyperlipidemia as well as fat storage in the liver and heart of rats consumed sucrose-rich diet.     

Green and black tea extracts inhibit HMG-CoA reductase and activate AMP kinase to decrease cholesterol synthesis in hepatoma cells

Recent studies have demonstrated that green and black tea consumption can lower serum cholesterol in animals and in man, and suppression of hepatic cholesterol synthesis is suggested to contribute to this effect. To evaluate this hypothesis, we measured cholesterol synthesis in cultured rat hepatoma cells in the presence of green and black tea extracts and selected components. Green and black tea decreased cholesterol synthesis by up to 55% and 78%, respectively, as measured by a 3-h incorporation of radiolabeled acetate. Inhibition was much less evident when radiolabeled mevalonate was used, suggesting that the inhibition was mediated largely at or above the level of HMG-CoA reductase. Both extracts directly inhibited HMG-CoA reductase when added to microsomal preparations, although the extent of inhibition was considerably less than the decrease in cholesterol synthesis observed in whole cells. As HMG-CoA reductase activity also can be decreased by enzyme phosphorylation by AMP kinase, the phosphorylation state of HMG-CoA reductase and AMP kinase, which is activated by phosphorylation, was determined in lysates from cells treated with tea extracts. Both extracts increased AMP-kinase phosphorylation and HMG-CoA reductase phosphorylation by 2.5- to 4-fold, but with different time courses: maximal phosphorylation with green tea was evident within 30 min of treatment, whereas with black tea phosphorylation was slower to develop, with maximal phosphorylation occurring > or =3 hours after treatment. These results suggest that both green and black tea decrease cholesterol synthesis in whole cells by directly inhibiting HMG-CoA reductase and by promoting its inactivation by AMP kinase.     

Potential mechanisms for the effects of tea extracts on the attachment,biofilm formation and cell size of Streptococcus mutans

Tea can inhibit the attachment of Streptococcus mutans to surfaces and subsequent biofilm formation. Five commercial tea extracts were screened for their ability to inhibit attachment and biofilm formation by two strains of S. mutans on glass and hydroxyapatite surfaces. The mechanisms of these effects were investigated using scanning electron microscopy (SEM) and phytochemical screening. The results indicated that extracts of oolong tea most effectively inhibited attachment and extracts of pu-erh tea most effectively inhibited biofilm formation. SEM images showed that the S. mutans cells treated with extracts of oolong tea, or grown in medium containing extracts of pu-erh tea, were coated with tea components and were larger with more rounded shapes. The coatings on the cells consisted of flavonoids, tannins and indolic compounds. The ratio of tannins to simple phenolics in each of the coating samples was ～3:1. This study suggests potential mechanisms by which tea components may inhibit the attachment and subsequent biofilm formation of S. mutans on tooth surfaces, such as modification of cell surface properties and blocking of the activity of proteins and the structures used by the bacteria to interact with surfaces.     

Extraction behavior of caffeine and EGCG from green and black tea

A dipping method was developed to extract the catechins (EGCG) and alkaloids (caffeine) from green tea (Korea) and black tea (Sri Lanka). The effects of the solvent composition (water vs. ethanol), extraction time, temperatures, and solvent pH on the amount of catechins (EGCG) and alkaloids (caffeine) extracted from green and black tea were investigated. Reversedphase high-performance liquid chromatography (RP-HPLC) was used to analyze the catechins (EGCG) and alkaloids (caffeine) extracted. The content of EGCG and caffeine in green tea extracts was in the range of 2.04∼0.30 and 10.22∼0.85 mg/g, respectively. The amount of EGCG and caffeine in black tea extracts was in the range of 0.32∼0.24 and 5.26∼1.01 mg/g, respectively. The amount of caffeine extracted from green and black tea was greater than the amount of EGCG. Pure water is the best solvent for extracting EGCG and caffeine from green tea. The amount of caffeine extracted from green and black tea increased as the temperature, extraction time, and hydrogen ion concentration of the solvent increased. Although the amount of EGCG extracted from green tea increased as the temperature increased, the amount of EGCG extracted from black tea was not affected by temperature. The extraction of EGCG from both green and black tea was not affected by the hydrogen ion concentration of the solvent.     

Enzymatic tannase treatment of green tea increases in vitro inhibitory activity against N-nitrosation of dimethylamine

In vitro experiments were performed to test inhibition of nitrite-mediated N-nitrosation by individual catechins, green tea, and tannase-treated green tea extracts. The extent of inhibition was measured via nitrosamine formation. Green tea with or without tannase treatment was examined to study nitrosation inhibition in order to evaluate the inhibitory activities with the structural changes of catechins present in the extracts. The results showed that the tannase-treated green tea had a greater ability to inhibit the nitrosation than green tea and ascorbic acid did. The tannase-treated green tea strongly inhibited the formation of N-nitrosodimethylamine (NDMA). Among four major catechins tested, epigallocatechin blocked the N-nitrosation efficiently, and epigallocatechin gallate was more unstable than epigallocatechin at pH 2.0 or 8.0. These results suggest that the consumption of tannase-treated green tea can reduce NDMA formation.     

Further investigation of the biosynthesis of caffeine in tea plants (Camellia sinensis L.). Methylation of transfer ribonucleic acid by tea leaf extracts.

1. The tRNA methyltransferase activity in vitro of leaves, cotyledons and roots of 85-day-old tea seedlings was studied. 2. The activity of extracts prepared from tea leaves with Polycar AT (insoluble polyvinylpyrrolidine) had optimum pH7.7 and was greatly influenced by thiol compounds, but only slightly by metal ions and ammonium acetate. 3. The activities of extracts, expressed per mg of protein, were as follows: roots greater than leaves greater than cotyledons. The only methylated base isolated after incubation with these preparations was 1-methyladenine. 4. The results did not support the view of involvement of methylation of nucleic acids in caffeine biosynthesis in tea plants. In contrast, it is suggested that theophylline is synthesized from the specific methylated precursor in nucleic acids, namely 1-methyladenylic acid, via 1-methylxanthine.     

茶黄毒蛾Euproctis pseudoconspersa(Strand)性外激素的分离鉴定和合成(英)

茶黄毒蛾是中国南方茶树上的重要害虫,其性引诱外激素经鉴定为10,14——二甲基十五碳异丁酸酯。本研究发展了一种外消旋式外激素合成法。装有40-1000μg的诱芯能够诱扑雄蛾。合成外激素的引诱性能相当于未交配雌蛾或雌蛾提取物。     

ISOLATION, IDENTIFICATION AND SYNTHESIS OF THE FEMALE SEX PHEROMONE OF THE TEA TUSSOCK MOTH, EUPROCTIS PSEUDOCONSPERSA (LEPIDOPTERA: LYMANTRIDAE)

Abstract The sex attractant pheromone of the tea tussock moth, a serious economic pest of tea plantations in southern China, has been identified as 10,14-dimethylpentadecyl isobutyrate. A synthesis of the racemic form of the pheromone was developed, and traps baited with the synthetic compound at doses of 40–1000 micrograms captured male moths. The synthetic pheromone was as effective as a trap bait as, virgin female moths, or extracts of female moths.     

Anticlastogenic effects of black tea (World blend) and its two active polyphenols theaflavins and thearubigins in vivo in Swiss albino mice.

This study investigated the inhibition of cyclophosphamide (CP) and dimethylbenz(a)anthracene (DMBA) induced genetic damage by black tea (World blend) and its two active polyphenols theaflavins (TF) and thearubigins (TR) in Swiss albino mice as measured by chromosome aberrations (CA) and sister chromatid exchanges (SCE). Three different concentrations (5, 10 and 20%) of tea and a single dose of TF and TR were tested for their anticlastogenic effects against DMBA (50 mg/kg body weight) and CP (20 mg/kg for CA and 10 mg/kg for SCE). A significant decrease in CA was observed in all the three concentrations of tea extract plus DMBA treated groups when compared with the respective DMBA treated group alone. Similarly a significant decrease in CA was observed in all the three concentrations of tea extracts plus CP treated series when compared with the group treated with CP alone. In SCE assay, a significant decrease in SCE was observed in 5, 10 and 20% black tea extract plus CP and 10 and 20% tea extracts plus DMBA treated groups when compared with the CP or DMBA treated group alone. In the single dose of TF and TR treated groups a significant decrease in both CA and SCE was observed in both the TF and TR plus both the carcinogen treated groups when compared with their positive controls. The protective effects of black tea extracts were more significant than that of its two polyphenols. This study indicates that both black tea and its active polyphenols TF and TR have significant anticlastogenic effects in bone marrow cells of mice.     

Ilex paraguariensis extracts are potent inhibitors of nitrosative stress: a comparative study with green tea and wines using a protein nitration model and mammalian cell cytotoxicity

Due to the increasing importance of nitrosative stress in pathology and the efficacy displayed by flavonoids in cancelling the effects of peroxynitrite, we decided to conduct a comparative study of three commonly used beverages with the highest polyphenol contents and proven antioxidant properties: mate (Ilex paraguariensis); green tea (Camelia sinensis) extracts and white and red wines of the main varietals. We directly evaluated and compared the extracts and wines as protein nitration inhibitors using 3-nitrotyrosine as a biomarker, we studied the extracts as protectors from OONO-induced cytotoxicity in two mammalian cell lines. Both green tea and mate extracts have a high polyphenol content, in the case of Ip, its higher concentration and higher free radical quenching activity on the DPPH assay may be mainly due to the sui generis extraction procedure. When BSA was incubated in the presence of SIN-1, a time and dose dependent nitration of the protein is clearly shown. Co-incubation of BSA with Ip, green tea or red wines led to a dose dependent inhibition of the effect. Ip displayed the highest inhibitory activity, followed by red wines and the green tea. Dilutions as low as 1/1500 produced more than 80% inhibition of albumin nitration. When we studied peroxynitrite-induced cytotoxicity in murine RAW 264.7 macrophages and 31EG4 mammary cells., we found a potent, dose-dependent protective effect that was Ilex paraguariensis > red wines > green tea. Taken together, our results indicate that when the herbal preparations studied here are prepared the way they are usually drunk, Ip displays the highest inhibition of protein nitration, and the highest promotion of cell survival, whereas green tea or red wines display significant but lesser effects at the same concentrations. Further studies aiming at isolation of the active principles and assessment of their bioavailability are warranted.