Evaluation of the Effect of Camellia Sinensis Extract on Amyloid Fibril Formation in Hen Egg-White Lysozyme and its Possible Mechanism in the Prevention of Alzheimer's Disease

Alzheimer’s disease (AD) is the most important neurodegenerative disorder, causing dementia in the elderly. Brain pathology of AD patients is characterized by deposits of amyloid plaques and neurofibrillary tangles. There is a great deal of interest in developing inhibitors of amyloidogenic processes. In traditional herbal medicine, numerous plants are used to treat age-related cognitive disorders. Based on various studies, extracts of Camellia sinensis are rich in polyphenolic agents including caffeine, flavonoids, daidzein, and catechins. It has been suggested that polyphenols are capable of inhibiting amyloid fibril formation in vitro, regardless of oxidative conditions. This study aimed to explore the inhibitory activity of Camellia sinensis extract against the fibril formation of hen egg-white lysozyme (as an amyloidal model). In this experimental study, fiber was formed in hen egg-white lysozyme under acidic conditions at high temperature. Lysozyme (2 mg/mL) was dissolved in glycine buffer (50 mM) (pH=2.5) and incubated at 57 C for the specified durations, while being gently stirred. Various techniques including thioflavin T, Congo red absorbance assay, and atomic force microscopy were used to confirm fibrillation. Independent t-test and ANOVA were performed, using SPSS version 16. In the absence of Camellia sinensis extracts, soluble oligomers became evident after 24 hours of incubation, followed by the subsequent appearance of mature fibrils after 48 hours. Upon incubation with various extract concentrations (range = 0.1-1 mg/ml), formation of amyloid fibrils and oligomers was inhibited. The inhibition was dose-dependent and the best concentration was 1 mg/ml. Also, cytotoxicity of oligomers in the presence of the extract decreased, as indicated by the MTT assay. The findings indicated that polyphenols of Camellia sinensis extract may directly penetrate into the amyloidogenic core of early aggregates and inhibit amyloid fibril formation.