Tea Polyphenols in Parkinson's Disease.

Parkinson's disease (PD) is a common motor neurodegenerative disorder with multifactorial etiology that is an increasing burden on our aging society. PD is characterized by nigrostriatal degeneration which might involve oxidative stress, α-synuclein (αS) aggregation, dysregulation of redox metal homeostasis and neurotoxicity. Although the exact cause remains unknown, both genetic and environmental factors have been implicated. Among the various environmental factors tea consumption has attracted increasing interest, as besides being one of the most consumed beverages in the world, tea contains specific polyphenols which can play an important role in delaying the onset or halting the progression of PD. Green and black teas are rich sources of polyphenols, the most abundant being epigallocatechin-3-gallate (EGCG) and theaflavins. There is now consistent mechanistic data on the neuroprotective and neuroregenerative effects of tea polyphenols, indicating that they do not just possess anti-oxidant or anti-chelating properties but may directly interfere with aggregation of the αS protein and modulate intracellular signalling pathways, both in vitro and in animal models. EGCG in green tea has been by far the most studied compound and therefore future investigations should address more the effects of other polyphenols, especially theaflavins in black tea. Nevertheless, despite significant data on their potential neuroprotective effects, clinical studies are still very limited and to date only EGCG has reached phase II trials. This review collates the current knowledge of tea polyphenols and puts into perspective their potential to be considered as nutraceuticals that target various pathologies in PD.