Understanding the Broad-Spectrum Neuroprotective Action Profile of Green Tea Polyphenols in Aging and Neurodegenerative Diseases

During the last century, the world population has shown a staggering increase in its proportion of elderly members and thus, neurodegenerative diseases like Alzheimer's and Parkinson's diseases (AD and PD, respectively) are becoming an increasing burden. Brain aging and neurodegenerative diseases of the elderly are characterized by oxidative damage, dysregulation of redox metals homeostasis and inflammation, supporting a therapeutic use of antioxidants. Natural plant polyphenols (flavonoids and non-flavonoids) are the most abundant antioxidants in the diet and as such, are ideal nutraceuticals for neutralizing stress-induced free radicals and inflammation. Human epidemiological and new animal data suggest that green and black tea drinking (enriched in a class of flavonoids named catechins) may help protecting the aging brain and reduce the incidence of dementia, AD, and PD. Mechanistic studies on the neuroprotective/neuroregenerative effects of green tea catechins revealed that they act not only as antioxidants metal chelators, but also as modulators of intracellular neuronal signaling and metabolism, cell survival/death genes, and mitochondrial function. Thus, these dietary compounds are receiving significant attention as therapeutic multifunctional cytoprotective agents that simultaneously manipulate various brain targets. The scope of this review is to assess and put into perspective salient features of the beneficial brain action of natural, non-toxic green tea catechins in aging-impaired cognition and neurodegenerative diseases and to discuss a scenario concerning their potential, in drug combination, to target distinct pathologies, in the quest for a disease modifying therapy.