Cholinesterase Inhibitory and In Silico Toxicity Assessment of
Thirty-Four Isoquinoline Alkaloids - Berberine as the Lead Compound
Authors: Senol Deniz F. Sezer , Ekhteiari  Salmas Ramin , Emerce Esra , Sener Bilge , Orhan Ilkay Erdogan 
Published: April 2023

Background:
Cholinesterase (ChE) inhibitors used currently in clinics for the treatment of
Alzheimer’s disease (AD) are the most prescribed drug class with nitrogen-containing chemical formula.
Galanthamine, the latest generation anti-ChE drug, contains an isoquinoline structure.

Objective:
The aim of the current study was to investigate the inhibitory potential of thirty-four isoquinoline
alkaloids, e.g. (-)-adlumidine, β-allocryptopine, berberine, (+)-bicuculline, (-)-bicuculline,
(+)-bulbocapnine, (-)-canadine, (±)-chelidimerine, corydaldine, (±)-corydalidzine, (-)-corydalmine,
(+)-cularicine, dehydrocavidine, (+)-fumariline, (-)-fumarophycine, (+)-α-hydrastine, (+)-isoboldine,
13-methylcolumbamine, (-)-norjuziphine, norsanguinarine, (-)-ophiocarpine, (-)-ophiocarpine-Noxide,
oxocularine, oxosarcocapnine, palmatine, (+)-parfumine, protopine, (+)-reticuline, sanguinarine,
(+)-scoulerine, (±)-sibiricine, (±)-sibiricine acetate, (-)-sinactine, and (-)-stylopine isolated from
several Fumaria (fumitory) and Corydalis species towards acetyl- (AChE) and butyrylcholinesterase
(BChE) by microtiter plate assays. The alkaloids with strong ChE inhibition were proceeded to molecular
docking simulations as well as in silico toxicity screening for their mutagenic capacity through
VEGA QSAR (AMES test) consensus model and VEGA platform as statistical approaches. The inputs
were evaluated in a simplified molecular input-line entry system (SMILES).

Methods:
ChE inhibition assays indicated that the highest AChE inhibition was caused by berberine
(IC50: 0.72 ± 0.04 μg/mL), palmatine (IC50: 6.29 ± 0.61 μg/mL), β-allocryptopine (IC50: 10.62 ± 0.45
μg/mL), (-)-sinactine (IC50: 11.94 ± 0.44 μg/mL), and dehydrocavidine (IC50: 15.01 ± 1.87 μg/mL) as
compared to that of galanthamine (IC50: 0.74 ± 0.01 μg/mL), the reference drug with isoquinoline
skeleton. Less number of the tested alkaloids exhibited notable BChE inhibition. Among them, berberine
(IC50: 7.67 ± 0.36 μg/mL) and (-)-corydalmine (IC50: 7.78 ± 0.38 μg/mL) displayed a stronger inhibition
than that of galanthamine (IC50: 12.02 ± 0.25 μg/mL). The mutagenic activity was shown for
β-allocryptopine, (+)- and (-)-bicuculline, (±)-corydalidzine, (-)-corydalmine, (+)-cularicine, (-)-
fumarophycine, (-)-norjuziphine, (-)-ophiocarpine-N-oxide, (+)-scoulerine, (-)-sinactine, and (-)-
stylopine by means of in silico experiments.

Results:
The results obtained by molecular docking simulations of berberine, palmatine, and (-)-
corydalmine suggested that the estimated free ligand-binding energies of these compounds inside the
binding domains of their targets are reasonable to make them capable of establishing strong polar and
nonpolar bonds with the atoms of the active site amino acids.

Conclusion::
Our findings revealed that berberine, palmatin, and (-)-corydalmine stand out as the most
promising isoquinoline alkaloids in terms of ChE inhibition. Among them, berberine has displayed a
robust dual inhibition against both ChEs and could be evaluated further as a lead compound for AD.