EXTRACTION AND IN VITRO SCREENING OF POTENTIAL ACETYLCHOLINESTERASE, BUTYRYLCHOLINESTERASE AND BACE1 INHIBITORS FROM THE LEAVES OF OCIMUM SANCTUM

As part of our ongoing isolation of cholinesterase (ChE) and β-site amyloid precursor protein (APP) cleaving enzyme 1 (BACE1) inhibitors from natural sources, the bioactivity of the ethanolic extracts was screened for their inhibitory activities against acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and BACE1. Ocimum sanctum exhibited promising inhibitory activity against AChE, BChE, BACE1 and peroxynitrite (ONOO- ). Among the different solvent-soluble fractions obtained from the ethanolic extract, the dichloromethane (CH2Cl2) fraction was found to cause the most potent scavenging, or inhibitory activities, against peroxynitrite (ONOO- ) with the respective IC50 values of 1.21 ± 0.05 µg/mL. Likewise, the dichloromethane fraction also exhibited potent inhibitory activities against AChE, BChE and BACE1 with IC50 values of 2.54 ± 0.03, 13.52 ± 0.13 and 3.05 ± 0.01 µg/mL, respectively. Silica gel column chromatography of the dichloromethane fraction yielded two flavonoids, Cirsilineol and Isothymusin, based on the comparison with reported 1H- and 13C-NMR spectroscopic data. All of the compounds displayed concentration dependent in vitro inhibitory activity toward the ChEs, BACE1 and peroxynitrite (ONOO- ). Among them, Cirsilineol exhibited the potential inhibitory activity toward ChEs with the respective IC50 values of 2.95 ± 0.02 and 3.25 ± 0.08 µM, whereas the potential BACE1 inhibitor was Isothymusin with IC50 values of 4.45 ± 0.05 µM. In conclusion, we identified significant ChE and BACE1 inhibitors from Ocimum sanctum that could have value as new multitargeted compounds for anti-AD agents. Keywords: O. sanctum; Alzheimer's diseases; Antioxidant; Acetylcholinesterase; Butyrylcholinesterase; β-site amyloid precursor protein (APP) cleaving enzyme 1 (BACE1).