Chapter 22
Inhibition of Nitrosamine-Induced Tumorigenesis by Green Tea and Black Tea Zhi Yuan Wang, Jun-Yan Hong, Mou-Tuan Huang, Allan H. Conney, and Chung S. Yang Downloaded by CHINESE UNIV OF HONG KONG on March 7, 2016 | http://pubs.acs.org Publication Date: October 1, 1992 | doi: 10.1021/bk-1992-0507.ch022
1
Laboratory for Cancer Research, Department of Chemical Biology and Pharmacognosy, College of Pharmacy, Rutgers, The State University of New Jersey, Piscataway, NJ 08855-0789
Oral administration of green tea infusion (12.5 g tea leaves in 1 liter) as the sole source of drinking water to A / J mice markedly inhibited N -nitrosodiethylamine(NDEA)-induced tumorigenesis. It decreased lung tumor incidence and multiplicity and forestomach tumor multiplicity. Oral administration of decaffeinated green tea and black tea extracts (0.6%) also inhibited 4-(methylnitrosamino)-l-(3-pyridyl)-l-butanone (NNK)-induced lung tumorigenesis in A/J mice. When given during the N N K treatment period, both tea extracts decreased tumor multiplicity by about 65%. When given during the post-initiation period, decaffeinated green tea was more effective than decaffeinated black tea in the reduction of tumor multiplicity (85% vs. 63%) and tumor incidence (30% vs. 7%). Inhibitory effects of tea on esophageal tumorigenesis induced by N -nitrosomethylbenzylamine (NMBzA) or its precursors are also discussed.
Tea (Camellia sinensis) is one of the most popular beverages worldwide. Green tea is mainly consumed in Asian countries where tea is the major beverage, and black tea is mainly consumed in the Western nations and some Asian countries. Green tea is made by steaming and drying fresh tea leaves at elevated temperatures. Its composition is similar to that of fresh tea leaves and contains polyphenols (up to 30% of the dry weight), most of which are flavan-3-ols, commonly known as catechins. Some major components are (-)-epigallocatechin-3-gallate (EGCG), (-)epigallocatechin (ECG), (-)-epicatechin-3-gallate (EGC), (-)-epicatechin (EC), (+)gallocatechin, (+)-catechin, flavonols, anthocyanidins, caffeine, and gallic acid. The flavan-3-ols possess nucleophilic centers at positions 6 and 8. They have antioxidative properties due to their free radical trapping ability. In the manufacture of black tea, the monomelic flavan-3-ols undergo polyphenol oxidase-dependent oxidative polymerization via C-O or C-C bond formation leading to the production of theaflavins, thearubigins, and other oligomers which give the characteristic color and taste of black tea. 1
Corresponding author 0097-6156/92/0507-0292S06.00/0 © 1992 American Chemical Society
Huang et al.; Phenolic Compounds in Food and Their Effects on Health II ACS Symposium Series; American Chemical Society: Washington, DC, 1992.
22. WANG ET AL.
Inhibition of Nitrosamine-Induced Tumorigenesis
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Downloaded by CHINESE UNIV OF HONG KONG on March 7, 2016 | http://pubs.acs.org Publication Date: October 1, 1992 | doi: 10.1021/bk-1992-0507.ch022
Previous Studies on Tea and Cancer As summarized by the Committee on Diet and Health of the National Research Council (1) and a recent monograph by the International Agency for Research on Cancer (2), epidemiological studies on tea and cancer so far have yielded inconsistent and inconclusive results. For example, Kinlen et al. (3) reported a significant positive correlation between tea consumption and stomach cancer in a case-control study in London. However, in an earlier correlative study, there was a significant negative association between tea consumption and stomach cancer in both sexes in an investigation covering 20 countries (4). A case-control study in Nagoya, Japan indicated that black tea or green tea consumption did not increase the risk for stomach cancer (5). However, a case-control study in Kyushu, Japan showed that individuals consuming green tea more frequently or in larger quantities tended to have a lower risk for gastric cancer (6). Studies in Shizuoka Prefecture, Japan indicated that the cancer death rate in this tea production area, especially from stomach cancer, was lower than the national average, and inhabitants of towns having lower incidence rates tended to drink green tea more frequently than did inhabitants in other areas (7). Early reports indicated that tea extracts may have enhanced carcinogenesis in animals (8,9). For example, repeated subcutaneous injection of black tea extracts to rats once weekly for 45 to 77 weeks resulted in tumor formation at the injection site (8). Topical application of black tea infusion after initiation with benzo(a)pyrene resulted in weak tumor promotion (9). Recently, Nagabhushan et al. (10) reported that oral feeding of 60 °C tea infusions did not increase the tumor incidence, and subcutaneous injection of tea infusions failed to produce tumors in Swiss mice. Many recent studies have shown an inhibitory action of tea or tea components on carcinogenesis in animals. Application of polyphenols extracts of green tea to mouse skin inhibited the tumorigenicity of polycyclic aromatic hydrocarbons and tumor promotion by 12-0-tetradecanoylphorbol-13-acetate (TPA), teleocidin, andokadaic acid (11-14). Oral administration of a polyphenolic extract of green tea also significantly inhibited skin tumor initiation by 7,12-dimethylbenz(a)anthracene (12) and skin tumor promotion by TPA in mice (15). Oral feeding of E G C G in the drinking water during the post-initiation stage inhibited N-ethyl-W-nitro-Nnitrosoguanidine-induced tumor formation in the duodenum of mice (16). In additional studies, oral administration of a green tea polyphenol fraction (17) or green tea infusion (15) inhibited ultraviolet light - induced skin carcinogenesis in SKH-1 mice. However, the active compounds responsible for the inhibitory effects observed and the mechanisms of the inhibition remain to be investigated. In this communication, the effects of tea on NDEA-, N N K - , and NMBzA-induced carcinogenesis are discussed. NDEA, a commonly used carcinogen in animal studies, has been found in the environment. N N K , a potent tobacco carcinogen, is believed to be an important etiological factor in human carcinogenesis (18). Although it remains to be confirmed, the presence of N M B z A , a potent esophageal carcinogen in rats, in the human diet in a high esophageal cancer incidence area in northern China has been reported (19). Preparation and Compositions of Green Tea Infusion and Decaffeinated Tea Extracts Green tea leaves (12.5 g) were placed in 500 ml of freshly boiled deionized water for 15 min and then filtered. The tea leaves were steeped a second time with 500 ml of freshly boiled water and filtered. The combined filtrate is referred to as 1.25%
Huang et al.; Phenolic Compounds in Food and Their Effects on Health II ACS Symposium Series; American Chemical Society: Washington, DC, 1992.
Downloaded by CHINESE UNIV OF HONG KONG on March 7, 2016 | http://pubs.acs.org Publication Date: October 1, 1992 | doi: 10.1021/bk-1992-0507.ch022
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PHENOLIC COMPOUNDS IN FOOD AND THEIR EFFECTS ON HEALTH II
infusion. A 0.63% infusion was prepared from the 1.25% infusion via a 1 to 2 dilution. The amount of solids present in the 1.25% infusion was 4.69 mg/ml. E G C G , caffeine, E G C , E C G , and E C were the major components, accounting for 15.1%, 8.1%, 6.9%, 3.0%, and 1.8% of the dry solid, respectively. Decaffeinated green tea powder and black tea powder were dehydrated water extracts from decaffeinated tea leaves, and were supplied by the Thomas J. Lipton Company (Englewood Cliffs, NJ). The decaffeinated tea leaves were prepared by extracting tea leaves with supercritical C O 2 . E G C G , E G C , E C G and E C were the major catechins in decaffeinated green tea powder accounting for 11.1%, 11.0%, 2.6% and 3.1% of the dry weight, respectively, and caffeine was decreased to 0.3% of the dry weight. In the decaffeinated black tea powder, the amounts of E G C G , E G C , E C G , E C , and caffeine were 2.2%, 0.9%, 1.3%, 0.9%, and 0.4% of the dry weight, respectively. The amounts of theaflavins were 1.7% and thearubigins were about 12% of the dry weight. Induction and Inhibition of Tumorigenesis Female A/J mice (6-8 weeks old) were fed AIN-76A diet and given N D E A (10 mg/kg body weight) by gavage once weekly for 8 weeks or a single dose of N N K (103 mg/kg in saline, i.p.). The mice were given tea infusions or extracts as the sole source of drinking water during the "initiation" period (starting two weeks before and until one week after the carcinogen treatment), die post-initiation period (starting one week after carcinogen treatment and continuing until the end of the experiment), or the un tire experimental period. The mice were killed 16 weeks after the last dose of carcinogen treatment; tumors in the lung and forestomach were counted. Effects of O r a l Administration of Green Tea on NDEA-Induced L u n g and Forestomach Tumorigenesis Treatment of A/J mice with N D E A caused lung tumors in more than 90% of the animals with an average of 8.3 ± 1 . 0 tumors per mouse 16 weeks after the last dose of N D E A (Table I). The administration of 0.63% or 1.25% of green tea infusion as the sole source of drinking water during the NDEΑ-treatment (initiation) period, postinitiation period, or the entire experimental period significantly decreased the forestomach tumor multiplicity (by 31% to 63%) and lung tumor multiplicity (by 36% to 60%). The 1.25% green tea infusion also decreased lung tumor incidence in all three protocols (by 36 to 44%) and significantly decreased forestomach tumor incidence when given during the initiation period or the entire experimental period. Inhibitory effects on lung and forestomach tumorigenesis by green tea infusion were also observed in a similar experiment using a high dosage of N D E A (20 mg/kg). Histopathological examination showed that almost all lung tumors were pulmonary adenomas. Most of the forestomach lesions were hyperplasia or papilloma; carcinomain-situ and squamous cell carcinoma were also observed. In all the tea treatment groups, the incidence of papilloma was lower than the positive control group. It was observed that the tumor size was reduced in the tea-drinking animals. Effects of O r a l Administration of Decaffeinated Green Tea and Black Tea on NNK-Induced L u n g Tumorigenesis Treatment of A/J mice with a single dose of N N K (103 mg/kg) resulted in 96% of mice bearing lung tumors and an average multiplicity of 9.3 ± 1.3 tumors per mouse after 16 weeks (Table II). When 0.6% decaffeinated green tea or black tea was given during the NNK-treatment (initiation) period as the sole source of drinking water, tumor multiplicity was reduced by 67% or 65%, respectively. When the tea extract
Huang et al.; Phenolic Compounds in Food and Their Effects on Health II ACS Symposium Series; American Chemical Society: Washington, DC, 1992.
Huang et al.; Phenolic Compounds in Food and Their Effects on Health II ACS Symposium Series; American Chemical Society: Washington, DC, 1992.
30
47
2) G T (1.25%) alone
3) NDEA alone
93.6
0
10
30
5) GT(1.25%)
a
30
7) GT(1.25%)
60.0 (35.9%)
a
46.4* (50.4%)
36
9) GT(1.25%)
a
52.8 (43.6%)
a
76.7 (18.1%)
a
(36.1%) (60.0%)
b
1.0±0.3
1.4±0.3
b
(44.0%)
b
1.6±0.3
(52.0%)
b
1.2±0.3
(18.3%) (26.3%)
a
72.2
a
2
(59.0%) (62.7%)
b
b
3.4±0.6 3.1 ± 0 . 5
4.4±0.6 (8.1%) 90.0
a
(47.0%)
b
80.0
(34.9%)
b
3.5±0.5 5.4±0.6
(57.8%)
b
(1.5%)
(14.9%)
(31.3%)
b
96.4
83.3
(56.0%)
b
1.1 ± 0 . 3
97.0
1.6 ± 0.2b (36.0%)
5.7±0.7
8.3 ± 1.0
97.9
(0.9%)
0
0 2.5 ± 0.3
0
0
Tumors per mouse
0
The number of tumors is expressed as the mean ± S.E. and the % inhibition is shown in parentheses. p
