Tea antioxidants in cancer chemoprevention

Abstract

In recent years, the concept of cancer chemoprevention has matured greatly. Significant reversal or suppression of premalignancy in several sites by chemopreventive agents appears achievable. This article summarizes experimental data on chemopreventive effects of tea polyphenols in different tumor bioassay systems. Tea (Camellia sinensis) is cultivated in about 30 countries, and is the most widely consumed beverage in the world. Three main commercial tea varieties-green, black, and oolong-are usually consumed, but most experimental studies demonstrating the antimutagenic and anticarcinogenic effects of tea have been conducted with water extract of green tea, or a polyphenolic fraction isolated from green tea (GTP). The majority of these studies have been conducted in a mouse skin tumor model system where tea is fed either as water extract through drinking water, or as purified GTP. GTP has been shown to exhibit antimutagenic activity in vitro, and inhibit carcinogen-as well as UV-induced skin carcinogenesis in vivo. Tea consumption has also been shown to afford protection against chemical carcinogen-induced stomach, lung, esophagus, duodenum, pancreas, liver, breast, and colon carcinogenesis in specific bioassay models. Several epicatechin derivatives (polyphenols) present in green tea have been shown to possess anticarcinogenic activity; the most active is (Ϫ)-epigallocatechin-3-gallate, which is also the major constituent of GTP. The mechanisms of tea's broad cancer chemopreventive effects are not completely understood. Several theories have been put forward, including inhibition of UV-and tumor promoter-induced ornithine decarboxylase, cyclo-oxygenase, and lipoxygenase activities, antioxidant and free radical scavenging activity; enhancement of antioxidant (glutathione peroxidase, catalase, and quinone reductase) and phase II (glutathione-S-transferase) enzyme activities; inhibition of lipid peroxidation, and anti-inflammatory activity. These properties of tea polyphenols make them effective chemopreventive agents against the initiation, promotion, and progression stages of multistage carcinogenesis.

Natural phenolics in the prevention of UV-induced skin damage. A review

“…Tea (Camelia sinensis), one of the most consumed beverages in the world, is grown in about 30 countries 62 .…”

“…The major epicatechins found in green tea include (-)-epicatechin (EC), (-)-epicatechin-3-gallate (ECG), (-)-epigallocatechin (EGC), and (-)-epigallocatechin-3-gallate (EGCG) 13 . EGCG forms 60-70 % of the total amount of catechins 62 . These polyphenols have been shown to function as anti-inflammatory or anticarcinogenic agents in various biological systems.…”

Epigallocatechin gallate, a constituent of green tea, suppresses cytokine-induced pancreatic β-cell damage

“…Epigallocatechin gallate (EGCG), a major ingredient of green tea has been known to have a variety of physiological activities; anticarcinogenic, antioxidant, antiangiogenic, and antiviral activity (Nakayama et al, 1993;Yang and Wang, 1993;Katiyar and Mukhtar, 1997). In addition, EGCG was also reported to function as antidiabetic.…”

Modulatory influence of Green tea polyphenols on lipid peroxidation during L-Arginine induced acute pancreatitis in Wistar rats

“…Green tea extracts inhibit lipid peroxidation in in vitro systems and experimental animals [34,35,18]. Katiyar and Mukhtar, [36] suggested that, EGCG a component of Green Tea Polyphenols can interact with peroxyradicals and inhibit lipid peroxidation.…”