Isolation and Characterization of Acetylcholinesterase Inhibitors from Piper longum and Binding Mode Predictions

Abstract

Restoration of cholinergic function is considered a rational approach to enhance cognitive performance. Acetylcholinesterase inhibitors are still the best therapeutic option for Alzheimerʼs disease. The fruits of Piper longum have been used in traditional medicines for the treatment of memory loss. It was demonstrated that the dichloromethane extract of these fruits is able to inhibit acetylcholinesterase. Thus, the aim of this study was to identify the contained acetylcholinesterase inhibitors. The active zones were presented via TLC-bioautography, and five compounds were isolated in the process of a bioassay-guided phytochemical investigation. Their structures were characterized as piperine, methyl piperate, guineenisine, pipercide, and pellitorine using spectroscopy and spectrometry methods (UV, IR, MS, 1H-, and 13C-NMR). In vitro acetylcholinesterase inhibitory activities of the isolates and their IC50 values were determined via a colorimetric assay. Three of them exhibited enzyme inhibitory activities, with piperine being the most potent compound (IC50 of 0.3 mM). In order to investigate the binding mode of the tested compounds, docking studies were performed using the X-ray crystal structure of acetylcholinesterase from Tetronarce californica with the Protein Data Bank code 1EVE. The content of the active compounds in the extract was determined by a developed HPLC method. Piperine was present in the maximum quantity in the fruits (0.57%), whereas methyl piperate contained the minimum content (0.10%).

Insights into the Phytochemical and Multifunctional Biological Profile of Spices from the Genus Piper

“…For instance, the ethyl acetate extract of P. nigrum exhibited efficient inhibition percentages of 61.5% against AChE and 90.6% against BChE at 100 μg/mL, whereas from the 21 isolated piperamides, piperine was the most potent inhibitor with IC50 values of 63.16 μg/mL in AChE and 25.11 μg/mL in BChE, respectively [43]. On the other hand, the dichloromethane extract of P. longum, as well as piperine (IC50 = 0.32 mM), pipercide (IC50 = 0.61 mM) and guineensine (IC50 = 1.61 mM), were shown to be able to inhibit AChE [44]. In another study, the methanolic extracts obtained from the fruits of P. nigrum and P. retrofractum displayed IC50 values of 11.13 and 14.08 μg/mL against AChE, respectively [45].…”

Piper longum L.: A comprehensive review on traditional uses, phytochemistry, pharmacology, and health‐promoting activities

“…Acetylcholinesterase (AChE) inhibitors are thought to be the best therapeutic option for AD to date. Dichloromethane extract of the fruits was found to inhibit AChE which was observed via thin layer chromatography (TLC)‐bio‐autography (Khatami et al, 2020).…”