Studie zur Vorbeugung von
Darmpolypen mit Grüntee-Extrakt

Minimizing the risk of metachronous adenomas of the colorectum with green tea extract (MIRACLE): a randomised controlled trial of green tea extract versus placebo for nutriprevention of metachronous colon adenomas in the elderly population.

Background

The use of nutritional compounds for disease prevention and health maintenance is an emerging field, since nutritional products are usually less afflicted with the risk of severe side effects, and long-term experience in humans exists. Especially for cancer prevention, associations between diet and lifestyle have been established [1].

Green tea belongs to the oldest drinks of mankind, and its high levels of bioactive polyphenols provide the potential for therapeutic and preventive application. Supplementation of diet with green tea polyphenols as a nutraceutical has already been studied in the context of cancer, diabetes and cardiovascular disease [2-7].

About 30% of the content of green tea is polyphenols. The monomer flavan-3-ols are called catechins, and contribute to the astringent/bitter taste of green tea. Among all catechins in green tea the most important are 59% (-)-epigallocatechin-3-gallate (EGCG), 19% (-)-epigallocatechin (EGC), 13.6% (-)-Epicatechin-3-gallate (ECG), and 6.4% (-)-epicatechin (EC) [8].

Due to its presumed beneficial effects on cancer initiation and early cancer progression green tea polyphenols might be especially suited for cancer prevention rather than for cancer treatment [9]. The majority of colorectal cancers, the most frequent cancer type in men, shows a slow progression from normal mucosa to adenoma or advanced lesion (adenoma-carcinoma sequence), therefore allowing efforts for prevention of colorectal cancer [10]. Several studies on the chemoprevention of colorectal cancer have been performed using compounds such as acetyl salicylic acid (ASS) or cyclooxygenase (COX) isoenzyme 2-specific nonsteroidal anti-inflammatory agents (NSAIDs) [11-17]. NSAIDs seem to have a beneficial effect in preventing the development and/or recurrence of adenomas. However, the benefit risk ratio of daily use of these agents over years does not seem to justify a broad use for primary or secondary chemoprevention due to adverse effects such as gastrointestinal hemorrhage, peptic ulcers and potential cardiovascular toxicity [18]. Therefore, COX inhibitors have been accepted as chemopreventive agents only for patients with a very high risk of developing colorectal cancer, such as those with familial adenomatous polyposis [19].

Green tea extract and its major active component EGCG have been studied in several models for their preventive properties on the development of colon adenomas. In the Apcmin mouse, a model for colon adenoma development, a tremendous effect on the number and growth of adenomas was detected upon feeding the animals with EGCG-supplemented drinking water [20,21].

In addition, EGCG even inhibits the growth of established human colorectal cancer cells and induces apoptosis, which is accompanied by inhibition of COX-2 expression and reduced activation of the epidermal growth factor receptor tyrosine kinase family [22,23].

One small pilot study on the supplementation of green tea consumption with capsules containing green tea extract in Japanese patients with a history of colon adenomas resulted in a 50% reduction of the incidence of metachronous adenomas in the supplementation group compared to the placebo group after one year [9]. Epidemiological studies in Asian countries also point to a preventive effect on colon cancer from high daily intake of green tea (more than 5 cups daily) [24,25].

Since green tea extract - in contrast to green tea itself - is decaffeinated, diet supplementation with EGCG from green tea extract may constitute a nutriprevention with an extremely favorable safety profile. We report here on the design of a large, placebo-controlled prospective trial on the effect of diet supplementation with EGCG on colorectal adenoma prevention.

Nach oben

zum Seitenanfang