Objective: To determine the antimalarial activity of ethanol crude extracts from 20 Thai herbs against Plasmodium
falciparum (P. falciparum) chloroquine-resistant strain TM267. Molecular docking of the active compounds from the selected Thaiherbs were analyzed with Plasmodium falciparum dihydrofolate reductase (PfDHFR).
Material and Method: An in vitro study of antimalarial activity against P. falciparum TM267 was done using a parasite
lactate dehydrogenese assay, and the cytotoxic effects of extracts were tested against Vero cells using a 3-(4,5-
dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. The 50% inhibitory concentration (IC50) and 50%
cytotoxicity concentration were calculated from the dose-response curves. Molecular docking and post-docking
were analyzed with the x-ray crystal structure of PfDHFR-thymidylate synthase complexed with pyrimethamine,
nicotinamide adenine dinucleotide phosphate and deoxyuridylate.
Results: Of these, the Plumbago indica L. root extract showed high antimalarial activity, with an IC50 value of 3.7
μg/ml and less cytotoxicity when tested against Vero cells, followed by the Citrus hystrix DC. fruit extract, Vitex trifolia
Linn. root extract, Ocimum sanctum L. leave extract, of Allium sativum L. bulb extract and Salacia chinensis L. stem extract,
respectively. All 7 active compounds reported from these herbal extracts had high docking scores against PfDHFR.
The Citrusoside C from Citrus hystrix DC. had the highest docking score.
Conclusion: It could be purposed that there were active compounds in Plumbago indica L., Vitex trifolia Linn. and Citrus hystrix DC. which are potential inhibitors against malaria that could bind to the active site of PfDHFR. However, the active Citrusosides from Citrus hystrix DC. should be further investigated for their effectiveness against malaria.