UK research suggests that digestion of green tea by gut enzymes produces chemicals that may be more effective against Alzheimer's disease and cancer than those in undigested tea. Previous studies have shown that green tea polyphenols possess neuroprotective properties, protecting the brain by binding with the toxic compounds hydrogen peroxide and beta-amyloid, which play a significant role in the development of Alzheimer's disease. On ingestion, green tea polyphenols are metabolised and undergo bio-transformation which affects their bioavailability and therefore efficacy. In the new study, a green tea extract was subjected to a simulated gastrointestinal digestion and a 'colon-available' extract (CAGTE) prepared which represented the green tea phytochemicals potentially available after upper gastrointestinal digestion. CAGTE was assessed for its potential protective effects against hydrogen peroxide and beta-amyloid induced cytotoxicity in neuronal cells. CAGTE was found to protect cells at lower concentration ranges than polyphenol extracts from undigested tea. At high concentrations, CAGTE also exhibited direct anti-proliferative effects on tumour cells. (In vitro protective effects of colon-available extract of Camellia sinensis (tea) against hydrogen peroxide and beta-amyloid (Aβ((1-42))) induced cytotoxicity in differentiated PC12 cells. Phytomedicine. 2010 Dec 21. [Epub ahead of print]).