Synergistic inhibition on acetylcholinesterase by the combination of berberine and palmatine originally isolated from Chinese medicinal herbs

Alzheimer's disease is a multi-factorial neurodegenerative disorder devastatingly affecting the aged population worldwide. Previous studies have shown that medicinal herbs used in traditional Chinese medicine might be benefit to Alzheimer's disease patients. Berberine and palmatine, two isoquinoline alkaloids found in several medicinal herbs, were used for memory enhancement in China. In this study, the inhibitory effects of combined berberine and palmatine on acetylcholinesteras were evaluated using recombinant human acetylcholinesterase. Our results showed that the combination of berberine and palmatine inhibited acetylcholinesterase in a mixed competitive pattern. By the median-effect principle, the calculated combination index of the combination was less than 1, suggesting that berberine and plamatine inhibited acetylcholinesterase synergistically. Furthermore, the drug-reducing index of berberine and palmatine were 2.98 and 2.66, respectively. Taken together, the results showed that the combination of the two alkaloids might potentially be developed as a more effective therapeutic strategy for Alzheimer's disease patients.