Anti-Acetylcholinesterase Activities of Mono-Herbal Extracts and Exhibited Synergistic Effects of the Phytoconstituents: A Biochemical and Computational Study

Abstract

Alzheimer's disease (AD), a neurodegenerative disease, is the most common form of dementia. Inhibition of acetylcholinesterase (AChE) is a common strategy for the treatment of AD. In this study, aqueous, hydro-methanolic, and methanolic extracts of five potent herbal extracts were tested for their in vitro anti-AChE activity. Among all, the <i>Tinospora cordifolia</i> (Giloy) methanolic fraction performed better with an IC₅₀ of 202.64 µg/mL. Of the HPLC analyzed components of <i>T. cordifolia</i> (methanolic extract), palmatine and berberine performed better (IC₅₀ 0.66 and 0.94 µg/mL, respectively) as compared to gallic acid and the tool compound "galantamine hydrobromide" (IC₅₀ 7.89 and 1.45 µg/mL, respectively). Mode of inhibition of palmatine and berberine was non-competitive, while the mode was competitive for the tool compound. Combinations of individual alkaloids palmatine and berberine resulted in a synergistic effect for AChE inhibition. Therefore, the AChE inhibition by the methanolic extract of <i>T. cordifolia</i> was probably due to the synergism of the isoquinoline alkaloids. Upon molecular docking, it was observed that palmatine and berberine preferred the peripheral anionic site (PAS) of AChE, with π-interactions to PAS residue Trp286, indicating that it may hinder the substrate binding by partially blocking the entrance of the gorge of the active site or the product release.