Studies performed on genetically developed Alzheimer's disease mice suggest that epigallocatechin-3-gallate (EGCG), a polyphenolic compound of green tea could be a beneficial agent in the prevention of or progression of Alzheimer's disease.

Alzheimer's disease is characterized by the accumulation of amyloid plaques in the brain. Amyloid beta appears to be the main constituent of amyloid plaques in the brains of Alzheimer's disease patients.

Amyloid beta is a protein fragment derived from the amyloid precursor protein (APP) by the enzymes: alpha-secretase, beta-secretase and gamma-secretase. In a healthy brain, these fragments are broken down and eliminated. In Alzheimer's disease, the fragments accumulate to form amyloid plaques.

Compounds that enhance alpha-secretase, but inhibit beta or gamma-secretase activity, have therapeutic potential in the treatment of Alzheimer's disease.

Green tea, or its major polyphenolic compound, EGCG has been shown to have neuro protective effects.

In this study, researchers investigated the possible effects of EGCG on memory dysfunction caused by amyloid beta through the change of amyloid beta induced secretase activities.

Mice were pretreated with EGCG for 3 weeks before intracerebroventricular administration of amyloid beta. EGCG reduced the amyloid beta induced memory dysfunction, which was evaluated using passive avoidance and water maze tests. Amyloid beta induced a decrease in brain alpha-secretase and increases in both brain beta and gamma-secretase activities, which were both reduced by EGCG.

EGCG also inhibited amyloid beta induced apoptotic neuronal cell death in the brain. To further test the ability of EGCG to affect memory, EGCG was administered in drinking water for 1 week to the genetically developed Alzheimer's disease mice. Compared with untreated Alzheimer's disease mice, treatment with EGCG enhanced memory function and brain alpha-secretase activity but reduced brain beta and gamma-secretase activities as well as amyloid beta levels.
References:
1. Jae Woong Lee, et al. Green Tea-Epigallocatechin-3-Gallate Inhibits β-Amyloid-Induced Cognitive Dysfunction through Modification of Secretase Activity via Inhibition of ERK and NF-{kappa}B Pathways in Mice. J. Nutr. (August 5, 2009). doi:10.3945/jn.109.109785.