Inhibitory effects and toxicity of green tea polyphenols for gastrointestinal carcinogenesis.
BACKGROUND
Recently, and 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-nitroguanidine (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 GRE inhibited chemical carcinogenesis of the gastrointestinal tract in rodents. 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.
Yamane
T
T
First Department of Surgery, Kyoto Prefectural University of Medicine, Japan.
Nakatani
H
H
Kikuoka
N
N
Matsumoto
H
H
Iwata
Y
Y
Kitao
Y
Y
Oya
K
K
Takahashi
T
T
D000818:Animals; D016588:Anticarcinogenic Agents / Q000627:therapeutic use*; D001397:Azoxymethane; D002273:Carcinogens / Q000633:toxicity*; D002392:Catechin / Q000031:analogs & derivatives* / Q000627:therapeutic use / Q000633:toxicity; D005770:Gastrointestinal Neoplasms / Q000139:chemically induced* / Q000517:prevention & control*; D008297:Male; D008769:Methylnitronitrosoguanidine / Q000031:analogs & derivatives; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D009152:Mutagenicity Tests; D010936:Plant Extracts / Q000627:therapeutic use* / Q000633:toxicity*; D051381:Rats; D011916:Rats, Inbred F344; D017207:Rats, Sprague-Dawley; D013662:Tea
D016588:Anticarcinogenic Agents; D002273:Carcinogens; D010936:Plant Extracts; D013662:Tea; D008769:Methylnitronitrosoguanidine; C013525:ENNG; D002392:Catechin; C045651:epigallocatechin gallate; D001397:Azoxymethane