Acetyl- and butyryl-cholinesterase inhibitory activities of the edible brown alga Eisenia bicyclis

As part of our ongoing isolation of cholinester- ase (ChE) inhibitors from natural marine sources, the bio- activity of the ethanolic extracts from 12 Korean seaweeds were screened for their inhibitory activities against acetyl- cholinesterase (AChE), butyrylcholinesterase (BChE), and total reactive oxygen species (ROS) generation. Eisenia bi- cyclis exhibited promising inhibitory properties against AChE, BChE and total ROS with inhibition percentages (%) of 68.01 ± 1.37, 95.72 ± 3.80, and 73.20 ± 1.82 at con- centrations of 25 lg/mL, respectively. Among the different solvent-soluble fractions obtained from the ethanolic extract, the ethyl acetate (EtOAc) fraction was found to cause the most potent scavenging, or inhibitory activities, against 2,2-diphenyl-1-picrylhydrazyl (DPPH), peroxynitrite (ONOO - ) and total ROS with the respective IC50 values of 2.48 ± 0.01, 8.70 ± 0.06, and 0.81 ± 0.03 lg/mL. Like- wise, the EtOAc fraction also exhibited potent inhibitory activities against AChE and BChE with IC50 values of 2.78 ± 0.07 and 3.48 ± 0.32 lg/mL, respectively. Silica gel column chromatography of the EtOAc fraction yielded a phlorotannin, 974-B, based on the comparison with reported 1 H- and 13 C-NMR spectroscopic data. 974-B showed strong scavenging/or inhibitory potential against DPPH, ONOO - , total ROS, AChE, and BChE with the respective IC50 values of 0.86 ± 0.02, 1.80 ± 0.01, 6.45 ± 0.04, 1.95 ± 0.01, and 3.26 ± 0.08 lM, respectively. These results indicate that the potential of E. bicyclis and its phlorotannin for use in the development of therapeutic or preventive agents of Alzhei- mer's disease mainly through ChE inhibition and additional antioxidant capacities.