An effective agent for the treatment and/or prevention of Alzheimer's disease (AD) is needed due to the number of patients in the acute curve. In our research program to investigate effective agents for AD, we focused on crude drugs which consisted of incense sticks widely used in Asian countries including Japan. We selected 9 drugs as "aromatic" crude drugs and 2 as basal crude drugs. Among the samples tested, the essential oil obtained from the leaf of Cryptomeria japonica showed the most potent anti-acetylcholinesterase activity with 64.8% of inhibition at 100 μg/mL. In addition, no sample showed significant inhibition against β-secretase. From these results, the crude drugs selected in this study may be effective for AD therapy rather than prevention. The active principles of anti-acetylcholinesterase were investigated by activity-guided fractionation, and kaur-16-ene, nezukol and ferruginol were successfully identified, the IC 50 values were 640, 300 and 95 µM, respectively. Kaur-16-ene and nezukol inhibited acetylcholinesterase in the mixed type mode, while ferruginol inhibited it in the competitive mode. In addition, nezukol and ferruginol showed anti-butyrylcholinesterase activity, the IC 50 values were 155 and 22 μM, respectively. We also focused on the heartwood of Chamaecyparis obtusa, since this tree has been used as a building material for the heartwood of C. japonica. Ethyl acetate extract of C. obtusa showed anti-acetylcholinesterase activity of 37.7% inhibition at 100 μg/mL. The active principle was determined to be (-)-hinokinin by activity-guided fractionation and the IC 50 value was 176 μM. These results suggest that the leaf of C. japonica and heartwood of C. obtusa may be suitable agents for AD therapy when administered through the nasal system as an aroma supplement.

In our research program for investigating anti-dementia agents from natural plant resources, we screened extracts from 15 spice samples. Among the plant extracts tested, ethyl acetate extract prepared from rhizome of Zingiber zerumbet showed potent activity. Activity-guided purification led to determination of afzelin and its acetylated compound as the active principles. Afzelin showed moderate inhibitory activity against acetylcholinesterase and may also be expected to possess anti-butyrylcholinesterase activity. This is the first report to reveal the anti-cholinesterase activities of ethyl acetate extract of Z. zerumbet and afzelin. Furthermore, Z. zerumbet may be a potential therapeutic agent for the improvement of dementia, especially Alzheimer's disease.

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