Tea and cancer prevention: Molecular mechanisms and human relevance

Abstract

Tea made from the leaves of the plant Camellia sinensis is a popular beverage. The possible cancer preventive activity of tea and tea polyphenols has been studied extensively. This article briefly reviews studies in animal models, cell lines, and possible relevance of these studies to the prevention of human cancer. The cancer preventive activity of tea constituents have been demonstrated in many animal models including cancer of the skin, lung, oral cavity, esophagus, stomach, liver, pancreas, small intestine, colon, bladder, prostate, and mammary gland. The major active constituents are polyphenols, of which (-)-epigallocatechin-3-gallate (EGCG) is most abundant, most active, and most studied, and caffeine. The molecular mechanisms of the cancer preventive action, however, are just beginning to be understood. Studies in cell lines led to the proposal of many mechanisms on the action of EGCG. However, mechanisms based on studies with very high concentrations of EGCG may not be relevant to cancer prevention in vivo. The autooxidation of EGCG in cell culture may also produce activities that do not occur in many internal organs. In contrast to the cancer prevention activity demonstrated in different animal models, no such conclusion can be convincingly drawn from epidemiological studies on tea consumption and human cancers. Even though the human data are inconclusive, tea constituents may still be used for the prevention of cancer at selected organ sites if sufficient concentrations of the agent can be delivered to these organs. Some interesting examples in this area are discussed.

Epigallocatechin Gallate Suppresses Lung Cancer Cell Growth through Ras–GTPase-Activating Protein SH3 Domain-Binding Protein 1

“…Our data verify that EGCG is more effective in lung cancer cells that overexpress G3BP1 and not as effective in cells with low abundance of the G3BP1 protein. These results indicate that EGCG specifically targets G3BP1 to exert its chemopreventive effects, confirming other reports that EGCG suppresses anchorage-independent lung cancer cell growth (28). Our results provide strong evidence showing that G3BP1 is a direct mediator of EGCG suppression of anchorage-independent lung cancer cell growth.…”

“…Tea has been alleged to provide various beneficial health effects and medicinal efficacy in the prevention and treatment of many diseases (27). EGCG, the primary active ingredient in green tea, has been suggested to provide cancer-preventive activity by regulating multiple signaling transduction pathways as shown in cancer cell lines and animal models of cancer (28,29).…”

Improving the oral bioavailability of beneficial polyphenols through designed synergies

“…These phase 2 conjugation reactions are particularly important for polyphenols such as epi-gallocatechin-3-gallate (EGCG), which is the most abundant catechin in green tea. EGCG has numerous hydroxyl groups and undergoes extensive phase 2 metabolism, including glucuronidation, sulphation and methylation [37,88]. Several recent studies using liquid chromatography-tandem mass spectrometry (LC-MS/MS) have demonstrated that after ingestion of flavonoids, phase 2 conjugates of the aglycon such as glucuronides, sulphates and methylated metabolites predominate in the blood circulation, rather than the original plant glycoside or aglycon [32,93].…”

Green tea polyphenol epigallocatechin-3-gallate inhibits thrombin-induced hepatocellular carcinoma cell invasion and p42/p44-MAPKinase activation

“…More detailed, in vivo mouse studies have established that EGCG can function as a strong chemopreventative agent against cancer development and progression (47,48), and epidemiological and preclinical studies have demonstrated that catechins derived from green tea have profound chemopreventative and antitumor effects (38,48,49). The mechanisms by which EGCG is able to produce these effects is wide-ranging and includes e.g.…”