Polyphenol in green tea has cell-protecting capacity.

Green tea is one of the most popular and widely consumed beverages. It offers significant biological and pharmacological activity. Among the various bioactive ingredients found in green tea, the polyphenols exhibit potent antioxidant, antimutagenic, anticarcinogenic and anti-inflammatory properties.

Korean scientists examined the impact of heat processing and harvest time on the total phenolic content and radical scavenging capacity of Korean green tea extracts. To do so, the researchers used a olorimetric Folin-Ciocalteu assay and 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) or 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay, respectively. The scientists believe that epogallocatechin gallate (EGCG), a major polyphenol in green tea, could augment cellular antioxidant capacity, protecting certain cells in the body from oxidative damage. EGCG may provide preventive or therapeutic potential in the management of oxidative stress-mediated disorders.

Fresh green tea leaves were processed into steamed and roasted products using commercial processing. Seasonal variations of phenolic compounds in green tea were analyzed during the commercial harvest season of April to June 2005. The total phenolic levels and antioxidant capacity were higher in the steamed tea leaves than in the roasted ones. Green tea leaves harvested in April had lower levels of total phenolic content than those harvested in May and June.

In other tests, the scientists investigated the protective effect of EGCG against amyloid-induced oxidative damage in PC12 cells. PC12 cells that had experienced oxidative damage exhibited increased accumulation of intracellular reactive oxygen species (ROS) and underwent apoptotic death. ROS forms as a natural byproduct of the normal metabolism of oxygen and plays an important role in cell signaling. However, during times of environmental stress, ROS levels can increase dramatically, which can result in significant damage to cell structures. This evolves into oxidative stress, and EGCG caused stressed cells to die.

To further explore the possible molecular mechanisms underlying the antioxidant effects of EGCG, the scientists assessed the capability of EGCG to activate NF-E2-related factor 2 (Nrf2), a redox-sensitive transcription factor involved in protecting cells against oxidative stress. EGCG increased the DNA binding and transcriptional activity of Nrf2, leading to up-regulation of heme oxygenase-1, a representative antioxidant enzyme.

Further information. Young-Joon Surh, Department of Pharmacy, Seoul National University, San 56-1, Sillim-dong, Gwanak-gu 151-742 Seoul, Korea; phone: +82 2 880-7845; fax: +82 2 874-9775; email: surh@plaza.snu.ac.kr.