Screening for acetylcholinesterase inhibitory activity in plants used in Thai traditional rejuvenating and neurotonic remedies
Introduction
Alzheimer’s disease is a progressive degenerative neurologic disorder resulting in impaired memory and behavior. Epidemiological data indicate a potentially considerable increase in the prevalence of the disease over the next two decades (Johnson et al., 2000). Most treatment strategies have been based on the cholinergic hypothesis which postulated that memory impairments in patients suffering from this disease result from a deficit of cholinergic function in brain. One of the most promising approaches for treating this disease is to enhance the acetylcholine level in the brain using acetylcholinesterase (AChE) inhibitors (Enz et al., 1993).
Several AChE inhibitors are being investigated for the treatment of Alzheimer’s disease. However, only tacrine, donepezil, rivastigmine, and galanthamine have been approved by the Food and Drug Administration in the United States (Zarotsky et al., 2003). Until now, no drug of choice for the treatment of this disease has been decided. Therefore, the search for new AChE inhibitors is of great interest.
Nature is a rich source of biological and chemical diversity. The unique and complex structures of natural products cannot be obtained easily by chemical synthesis. A number of plants in Thailand have been used in traditional medicine remedies. For the study of drugs related to Alzheimer’s disease, we were interested in the Thai traditional remedies known as “rejuvenating” and “neurotonic” agents which have been popular in elderly. It is believed that these remedies can prevent forgetfulness and improve memory. The plants used in these remedies were screened for their AChE inhibitory activity using Ellman’s colorimetric method in 96-welled microplate (Ellman et al., 1961, Ingkaninan et al., 2000).
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Plant materials
The plant materials were collected from the north and central of Thailand. The voucher specimens are kept at Faculty of Pharmaceutical Sciences, Naresuan University, Phitsanulok and at PBM herbarium, Faculty of Pharmacy, Mahidol University, Bangkok. The plant materials were identified by Associate Professor Wongsatit Chuakul, Faculty of Pharmacy, Mahidol University, Bangkok, Thailand.
Extraction
The plant materials were cut into small pieces and dried in a hot air oven at 55 °C. The dried materials were
Results and discussion
Thirty-two plant materials reported as ingredients in Thai traditional rejuvenating and neurotonic remedies were collected. The methanolic extracts of these plants were tested for AChE inhibitory activity using Ellman’s colorimetric method in 96-welled microplate. The results are shown in Table 1. At the concentration of 0.1 mg/ml, the extracts from roots of Stephania suberosa Forman. and Tabernaemontana divaricata (L.) R.Br. ex Roem. & Schult. showed high AChE inhibitory activity (with percent
Conclusion
The methanolic extracts of plants used in Thai traditional rejuvenating and neurotonic remedies were screened for inhibitory activity on AChE. Of 32 plant extracts tested, the extracts from roots of Stephania suberosa and Tabernaemontana divaricata showed the highest inhibitory activity at the concentration of 0.1 mg/ml.
Acknowledgements
Financial supports by National Science and Technology Development Agency and International Foundation for Science are gratefully acknowledged. The authors thank Associate Professor Dr. Wongsatit Chuakul, Faculty of Pharmacy, Mahidol University, for the plant material identification.
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