Protective Effect of Green Tea Extract on Amyloid $\beta$ peptide-induced Neurotoxicity

Abstract Amyloid β peptide (A β ) is known to increase oxidative stress in nerve cells, leading to apoptosis that is characterized by free radical formation and lipid peroxidation. Neurodegenerative diseases such as Alzheimer’s disease (AD) are characterized by large deposits of A β in the brain. In our study, neuronal protective effects of green tea, along with water activity (0.813), and leaf storage periods (fresh leaf, or leaf stored for up to 4 weeks) were investigated. We measured protective effects against A β -induced cytotoxicity in neuron-like PC12 cells. Powdered green tea was extracted with distilled water at 70 ℃ for 5 min, and this extract was freeze-dried and stored at -20 ℃ until use. In cell viability assays using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), the fresh extract, and that obtained after 1 week of leaf storage, showed the best protective effects against A β -induced neurotoxicity. As oxidative stress causes membrane breakdown, the protective effect of green tea extracts was investigated using lactate dehydrogenase (LDH) and trypan blue exclusion assays. LDH release into the medium was inhibited (by 20-25%) in all tests. In addition, all green tea extracts (fresh, or stored before extraction for up to 4 weeks) showed better cell protective effects (93.3±1.8-96.2±2.4) than did vitamin C (91.0±1.6), used as a positive control. The results suggest that effectiveness of green tea extracts falls with prolonged leaf storage. Key words