Molecular Targets of Tannic Acid in Alzheimer's Disease

Tannic acid (TA) is a naturally occurring plant-derived polyphenol found in several herbaceous and woody plants, including legumes, sorghum, beans, bananas, persimmons, rasberries, wines and a broad selection of teas. Clinically, TA has strong antioxidant/free radical scavenging, antiinflammatory, anti-viral/bacterial, and anti-carcinogenic properties. While the aetiology of Alzheimer's disease (AD) remains unclear, this complex multifactorial neurodegenerative disorder remains the most common form of dementia, and is a growing public health concern worldwide. The neuroprotective effects of TA against AD have been shown in several in vitro and in vivo models of AD. Apart from its potent antioxidant and anti-inflammatory roles, evidence suggests that TA is also a natural inhibitor of β-secretase (BACE1) activity and protein expression. BACE1 is the primary enzyme responsible for the production and deposition of Aβ peptide. TA also destabilises neurotoxic amyloid beta (Aβ) fibrils in vitro. Apart from its effects on the Aβ cascade, TA can also inhibit the in vitro aggregation of tau peptide, a core component of intracellular neurofibrillary tangles (NFTs). This review summarizes the relevance of TA and TA-related vegetable extracts (tannins) in the pathogenesis of AD and its enzymatic targets. It also highlights the significance of TA as an important lead compound against AD.