Inhibition of acetylcholinesterase (AChE) and prevention of acetylcholine degradation are
of the most accepted therapies for Alzheimer’s disease. Aqueous extracts of seventeen Thai medicinal
plants were used in traditional Thai medicine for preventing chronic diseases such as diabetes, hypertension
and cardiovascular diseases. They were tested for cholinesterase inhibitory properties using the
Ellman’s colorimetric method. The extracts were screened for their free radical scavenging properties
using 1, 1 diphenyl-2-picrylhydrazyl (DPPH), ferric reducing antioxidant power (FRAP) and metal
chelating method. Total phenolic, total flavonoid, total tannin and total alkaloids contented in the extracts were determined.
The results found that Cassia siamea (CS) was the most potent inhibitor of AChE activity with IC50 value
0.85±0.06 mg/ ml. Lagerstroemia speciasa (LS) had the highest potency to scavenge DPPH radical with 50% scavenging
concentration (SC50) value 0.27±0.01 mg/ ml. CS and LS were high in reducing Fe3+ to Fe2+ with values 1.22± 0.06 and
1.49±0.02 mM of Fe2+ equivalent, respectively. 1 mg/ml of CS was the highest potency to inhibit AChE activity with
58.83±2.24%. Results showed AChE inhibition ability depended on the amount of total phenolic content. This study highlights
CS extract which showed highly potent inhibition of AChE and scavenging of free radicals. Clinical trials and active
compounds in CS should be studied for AD therapy in the other models.
Keywords: Thai medicinal plant, antioxidant, anticholinesterase, free radical scavenging, oxidative stress, phytochemical.
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