Green tea may offer therapeutic potential against oxidative stress-mediated disorders.

Green tea is one of the most popular and widely consumed beverages. It has a variety of biological and pharmacological activities. Its polyphenols exhibit potent antioxidant, antimutagenic, anticarcinogenic and anti-inflammatory properties.

Korean scientists examined how heat processing and harvest time can impact the total phenolic content and radical scavenging capacity of Korean green tea extracts. In their testing, the researchers used a commercial colorimetric assay and 2, 2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) or the 2, 2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay to make their determinations.

Seasonal variations of phenolic compounds in green tea were analyzed during the commercial harvest seasons from April to June 2005. Fresh green tea leaves were processed into steamed and roasted products by the researchers who followed commercial processing methods. The total phenolic levels and antioxidant capacity were greater 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 another experiment, the scientists investigated the protective effect of (-)-epogallocatechin-3-gallate (EGCG), a major green tea polyphenol, against amyloid-induced oxidative damage in PC12 cells. Some PC12 cells exhibited increased accumulation of intracellular reactive oxygen species (ROS) and underwent apoptotic death.

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

These results suggest that EGCG in green tea could augment cellular antioxidant capacity. This may provide preventive or therapeutic potential in the management of oxidative stress-mediated disorders.

As antioxidants, polyphenols protect cells and body chemicals against damage caused by free radicals that contribute to tissue damage in the body. For example, when low-density lipoprotein (LDL) cholesterol is oxidized, it can become glued to arteries and cause coronary heart disease. Polyphenols can also block the action of enzymes that cancers need for growth and they can deactivate substances that promote the growth of cancers. The polyphenol most strongly associated with cancer prevention is epigallocatechin-3-gallate, or EGCG.

Further information. Jung-Hee Jang, College of Pharmacy, Seoul National University, Shinlim-dong, Kwanak-ku, Seoul 151-742, Korea; phone: +82-2-877-3730; fax: +82-2-874-9775: URL: http://www.snupharm.ac.kr/eng/introduction/message.asp.