Phlorotannins from Ishige okamurae and their acetyl- and butyrylcholinesterase inhibitory effects

The inhibitory effects of phlorotannins isolated from Ishige okamurae on cholinesterase (acetylcholinesterase and butyrylcholinesterase) were evaluated. The methanolic (MeOH) extract and ethyl acetate (EtOAc) soluble fraction obtained from I. okamurae exhibited inhibitory effects against cholinesterase. Repeated column chromatography of the EtOAc fraction of I. okamurae resulted in the isolation of three phlorotannins. Their structures were elucidated on the basis of spectroscopic techniques (1D and 2D NMR) and characterized as phloroglucinol (1), 6,6′-bieckol (2) and diphlorethohydroxycarmalol (3), respectively. Among these, compound 2 exhibited inhibitory activity against acetylcholinesterase (AChE), with IC50 of 46.42 ± 1.19 μM. Compound 3 showed a moderate butyrylcholinesterase (BChE) inhibitory activity with IC50 value of 110.83 ± 1.15 μM. Compound 2 displayed noncompetative type inhibition against AChE when analyzed by Lineweaver-Burk plots of the inhibition kinetics. Thus, we suggest that compound 2 and I. okamurae, serve as a potential AChE inhibitors that could be used as potential functional food ingredients or nutraceuticals for preventing Alzheimer's disease.