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%).
Key words
Alzheimerʼs disease - AChE inhibitor -
Piper longum
- Piperaceae - piperine - pipercide - guineensine
